Association Between High Ambient Temperature and Risk of Stillbirth in California

Sex-specific effects of environmental temperature during gestation on fluctuating asymmetry in deciduous teeth

OBJECTIVES

External environmental heat exposure during gestation impacts the physiology of human development in utero, but evidence for these impacts has not yet been explored in dentition. We examined deciduous teeth for fluctuating asymmetry (FA), a measure of developmental instability, together with gestational environmental temperature data drawn from historical weather statistics.

MATERIALS AND METHODS

We measured dental casts from the longitudinal Burlington Growth Study, representing 172 participants (ages 3-6 years) with health records. FA was calculated from crown dimensions and intercuspal distances that develop during gestation. Multiple regression separated by sex (nfemale = 81) examined the effects of mean temperatures in each trimester, controlling for birth year.

RESULTS

In females, increased temperatures during the first trimester are significantly associated with an increase in FA (p = 0.03), specifically during the second and third prenatal months (p = 0.03). There is no relationship between temperature and FA for either sex in the second or third trimesters, when enamel is formed.

DISCUSSION

Dental instability may be sensitive to temperature in the first trimester in females during the scaffolding of crown shape and size in the earliest stages of tooth formation. Sexual dimorphism in growth investment strategies may explain the differences in results between males and females. Using enduring dental characteristics, these results advance our understanding of the effects of temperature on fetal physiology within a discrete period.

Impacts of heat and wildfire on preterm birth

BACKGROUND

Climate change continues to increase the frequency, intensity, and duration of heat events and wildfires, both of which are associated with adverse pregnancy outcomes. Few studies simultaneously evaluated exposures to these increasingly common exposures.

OBJECTIVES

We investigated the relationship between exposure to heat and wildfire smoke and preterm birth (PTB).

METHODS

In this time-stratified case-crossover study, participants consisted of 85,806 California singleton PTBs (20-36 gestational weeks) from May through October of 2015-2019. Birthing parent ZIP codes were linked to high-resolution daily weather, PM2.5 from wildfire smoke, and ambient air pollution data. Heat day was defined as a day with apparent temperature >98th percentile within each ZIP code and heat wave was defined as ≥2 consecutive heat days. Wildfire-smoke day was defined as a day with any exposure to wildfire-smoke PM2.5. Conditional logistic regression was used to calculate the odds ratio (OR) and 95% confidence intervals (CI) comparing exposures during a hazard period (lags 0-6) compared to control periods. Analyses were adjusted for relative humidity, fine particles, and ozone.

RESULTS

Wildfire-smoke days were associated with 3.0% increased odds of PTB (ORlag0: 1.03, CI: 1.00-1.05). Compared with white participants, associations appeared stronger among Black, Hispanic, Asian, and American Indians/Alaskan Native participants. Heatwave days (ORlag2: 1.07, CI: 1.02-1.13) were positively associated with PTB, with stronger associations among those simultaneously exposed to wildfire smoke days (ORlag2: 1.19, CI: 1.11-1.27). Similar findings were observed for heat days and when other temperature metrics (e.g., maximum, minimum) were used.

DISCUSSION

Heat and wildfire increased PTB risk with evidence of synergism. As the occurrence and co-occurrence of these events increase, exposure reduction among pregnant people is critical, especially among racial/ethnic minorities.

Temperature-related neonatal deaths attributable to climate change in 29 low- and middle-income countries

Exposure to high and low ambient temperatures increases the risk of neonatal mortality, but the contribution of climate change to temperature-related neonatal deaths is unknown. We use Demographic and Health Survey (DHS) data (n = 40,073) from 29 low- and middle-income countries to estimate the temperature-related burden of neonatal deaths between 2001 and 2019 that is attributable to climate change. We find that across all countries, 4.3% of neonatal deaths were associated with non-optimal temperatures. Climate change was responsible for 32% (range: 19-79%) of heat-related neonatal deaths, while reducing the respective cold-related burden by 30% (range: 10-63%). Climate change has impacted temperature-related neonatal deaths in all study countries, with most pronounced climate-induced losses from increased heat and gains from decreased cold observed in countries in sub-Saharan Africa. Future increases in global mean temperatures are expected to exacerbate the heat-related burden, which calls for ambitious mitigation and adaptation measures to safeguard the health of newborns.

Ambient temperature-related sex ratio at birth in historical urban populations: the example of the city of Poznań, 1848-1900

This study examines whether exposure to ambient temperature in nineteenth-century urban space affected the ratio of boys to girls at birth. Furthermore, we investigate the details of temperature effects timing upon sex ratio at birth. The research included 66,009 individual births, aggregated in subsequent months of births for the years 1847-1900, i.e. 33,922 boys and 32,087 girls. The statistical modelling of the probability of a girl being born is based on logistic GAM with penalized splines and automatically selected complexity. Our research emphasizes the significant effect of temperature in the year of conception: the higher the temperature was, the smaller probability of a girl being born was observed. There were also several significant temperature lags before conception and during pregnancy. Our findings indicate that in the past, ambient temperature, similar to psychological stress, hunger, malnutrition, and social and economic factors, influenced the viability of a foetus. Research on the effects of climate on the sex ratio in historical populations may allow for a better understanding of the relationship between environmental factors and reproduction, especially concerning historical populations since due to some cultural limitations, they were more prone to stronger environmental stressors than currently.

An expert review of environmental heat exposure and stillbirth in the face of climate change: Clinical implications and priority issues

Exposure to extreme heat in pregnancy increases the risk of stillbirth. Progress in reducing stillbirth rates has stalled, and populations are increasingly exposed to high temperatures and climate events that may further undermine health strategies. This narrative review summarises the current clinical and epidemiological evidence of the impact of maternal heat exposure on stillbirth risk. Out of 20 studies, 19 found an association between heat and stillbirth risk. Recent studies based in low- to middle-income countries and tropical settings add to the existing literature to demonstrate that all populations are at risk. Additionally, both short-term heat exposure and whole-pregnancy heat exposure increase the risk of stillbirth. A definitive threshold of effect has not been identified, as most studies define exposure as above the 90th centile of the usual temperature for that population. Therefore, the association between heat and stillbirth has been found with exposures from as low as >12.64°C up to >46.4°C. The pathophysiological pathways by which maternal heat exposure may lead to stillbirth, based on human and animal studies, include both placental and embryonic or fetal impacts. Although evidence gaps remain and further research is needed to characterise these mechanistic pathways in more detail, preliminary evidence suggests epigenetic changes, alteration in imprinted genes, congenital abnormalities, reduction in placental blood flow, size and function all play a part. Finally, we explore this topic from a public health perspective; we discuss and evaluate the current public health guidance on minimising the risk of extreme heat in the community. There is limited pregnancy-specific guidance within heatwave planning, and no evidence-based interventions have been established to prevent poor pregnancy outcomes. We highlight priority research questions to move forward in the field and specifically note the urgent need for evidence-based interventions that are sustainable.

The mediation of the placenta on the association between maternal ambient temperature exposure and birth weight

Studies have indicated that exposure to low and high temperatures during pregnancy negatively affects fetal development. The placenta plays vital functions in fetal development and could also be impacted by suboptimal temperatures. However, whether the placenta mediates the association between suboptimal temperature and birth weight is unknown. Our study aims to evaluate the association between ambient temperature and birth weight as well as the mediation effect of the placenta. A prospective birth cohort study was conducted during 2017-2020 in Guangzhou, China (n = 3349 participants). We defined extreme temperature exposure during the whole pregnancy by using different thresholds, including low temperatures (< 25th, < 15th, < 10th, < 5th percentiles), and high temperatures (> 75th, > 85th, > 90th, > 95th percentiles). Three different approaches (generalized linear model, inverse probability weighting, and doubly robust model) were applied to estimate the effects of low/high temperatures on birth weight and placental indicators, including placental weight, placental volume, and placental-to-birth weight ratio (PFR), respectively. We observed that both low and high ambient temperatures during the whole pregnancy were associated with lower birth weight and negative changes in placental indicators. The estimated lower mean birth weight ranged from -158 g (95 % CI: -192 g, -123 g) to -363 g (95 % CI: -424 g, -301 g) for low temperatures and from -97 g (95 % CI: -135 g, -59 g) to -664 g (95 % CI: -742 g, -585 g) for high temperatures. In mediation analyses, placental weight mediated 28.79 % to 40.47 % and 48.22 % to 54.38 % of the association of low and high temperatures with birth weight, respectively. The findings suggest that placental weight may mediate the association between ambient temperature exposure and birth weight.

The risk of miscarriage is associated with ambient temperature: evidence from coastal Bangladesh

Background

Exposure to high ambient temperature is reported to cause adverse pregnancy outcomes. However, considering myriad temperature and climatic conditions as well as different contextual factors, the paucity of studies from the developing regions impedes the development of a clear understanding of the heat-pregnancy outcome relationship.

Materials and methods

This study was conducted in Chakaria, a coastal region of Bangladesh, where International Centre for Diarrhoeal Disease Research, Bangladesh (icddr,b) administers a health and demographic surveillance system (HDSS). The surveillance workers visit the households every three months as a part of the routine surveillance activity. Between 2012 and 2020, the surveillance workers documented histories of 23,482 pregnancies among 13,376 women and the women were followed up for their pregnancy outcomes. The temperature records were obtained from the Bangladesh Meteorological Department's weather station at Cox's Bazar. The dates of pregnancy outcome were linked with the daily average temperature on the day of pregnancy outcome. A logistic regression model was employed to examine the relationship between temperature and the incidence of miscarriage.

Results

Out of 23,482 pregnancy outcomes, 3.7% were induced abortions. Among the remaining 22,624 pregnancy outcomes, 86.2% were live births, 10.7% were miscarriages and 3.1% were stillbirths. Miscarriages peaked between 8-14 weeks of gestation and varied according to temperature. For women exposed to temperatures between 28°C and 32°C, the risk of miscarriage was 25% greater (adjusted OR 1.25, 95% CI 1.07-1.47) compared to those exposed to temperatures from 16°C to 21°C.

Conclusion

The study establishes a connection between miscarriage and high ambient temperatures in a coastal region of Bangladesh. Implementing timely and appropriate adaptation strategies to prevent miscarriages is of paramount importance for a densely populated country like Bangladesh.

Extreme Temperature Exposure and Risks of Preterm Birth Subtypes Based on a Nationwide Survey in China

BACKGROUND

Previous studies have reported that ambient temperature may affect perinatal outcomes. However, whether extreme temperature affects the risk of preterm birth (PTB) remains controversial. Studies on the associations of extreme temperature with PTB subtypes are lacking.

OBJECTIVES

We aimed to investigate the associations of extreme climate events with the risks of PTB and its subtypes, discerning possible modifiers.

METHODS

Data on all singleton deliveries were obtained from the China Labor and Delivery Survey (CLDS), a nationwide investigation implemented in 2015 and 2016. PTB was defined as gestational weeks < 37 and then categorized as early (24-34 wk) and late PTBs (35-36 wk), and clinical subtypes [spontaneous PTB, preterm premature rupture of the fetal membranes (PPROM), iatrogenic PTB]. Ambient temperature data were provided by the China National Weather Data Sharing System. Five heat indexes and five cold indexes were used to define heat waves and cold spells. Generalized linear mixed models with a random term by hospital unit were used to assess the associations of short-term prenatal extreme temperature exposure. The Cox proportional hazard regression model was applied to assess the nonlinear associations of low- or high-temperature exposure at the whole and different trimesters of pregnancy with the risk of PTB. Stratified analyses were conducted to assess the possible modification by geographic region and fetal sex.

RESULTS

A total of 70,818 singleton births from 96 hospitals in China were included, among which 4,965 (7.01%) were PTBs. Exposure to extreme cold events 1 wk before delivery was associated with an increased PTB risk, with an adjusted odds ratio (aOR) [95% confidence intervals (CIs)] of 1.07 (95% CI: 1.04, 1.10) and 1.06 (1.04, 1.09) for the total days when the daily average temperature below the fifth percentile (fifth-days) and the 10th percentile (10th-days), 1.18 (1.04, 1.34) for the cold spells when the daily average temperature below the fifth percentile for two consecutive days (fifth-2D), 1.09 (1.03, 1.16) and 1.12 (1.06, 1.19) for the cold spells when the daily average temperature below the 10th percentile for three and two consecutive days (10th-3D and 10th-2D), respectively. Results of extreme temperature exposure during 2 weeks before delivery showed similarly significant associations. The association between cold spells and PTB tended to be stronger for late PTB than for early PTB. Cold spells were mainly associated with spontaneous PTB and late PPROM. A stratified analysis indicated that pregnant women in western and northern regions tended to be more sensitive to cold spells, and pregnant women with a female fetus appeared to be at a higher risk of PTB when exposed to cold spells. Pregnant women in late pregnancy were more susceptible to extreme temperatures. No significant or stable association was found between heat waves and preterm birth.

DISCUSSION

Exposure to cold spells was associated with an increased risk of PTB, especially late, spontaneous PTB and PPROM. The associations appeared to be more pronounced in the north and west regions and in pregnancies with female fetuses. https://doi.org/10.1289/EHP10831.

Maternal apparent temperature during pregnancy on the risk of offspring asthma and wheezing: effect, critical window, and modifiers

The objective of this study was to explore the impact of maternal AT during pregnancy on childhood asthma and wheezing, as well as the potential effect modifiers in this association. A cross-sectional study was implemented from December 2018 to March 2019 in Jinan to investigate the prevalence of childhood asthma and wheezing among aged 18 months to 3 years. Then, we conducted a case-control study based on population to explore the association between prenatal different AT exposure levels and childhood asthma and wheezing. The association was assessed by generalized additive models and logistic regression models, and stratified analyses were performed to explore potential effect modifiers. A total of 12,384 vaccinated children participated in screening for asthma and wheezing, 236 cases were screened, as well as 1445 controls were randomized. After adjusting for the covariates, childhood asthma and wheezing were significantly associated with cold exposure in the first trimester, with OR 1.731 (95% CI: 1.117-2.628), and cold exposure and heat exposure in the third trimester, with ORs 1.610 (95% CI: 1.030-2.473) and 2.039 (95% CI: 1.343-3.048). In the third trimester, enhanced impacts were found among girls, children whose distance of residence was close to the nearest main traffic road, and children whose parents have asthma. The study indicates that exposure to extreme AT during the first and third trimesters could increase the risk of childhood asthma and wheezing.

Climate Change and Pregnancy: Risks, Mitigation, Adaptation, and Resilience

Importance

Climate change is affecting the earth, resulting in more extreme temperatures and weather, rising sea levels, more frequent natural disasters, and displacement of populations of plants and animals, including people and insects. These changes affect food and housing security, vector-borne illnesses, and access to clean air and water, all of which influence human health.

Evidence and Results

There are a number of adverse health outcomes linked to heat, air pollution from wildfires, stress from natural disasters, and other elements of climate change. Pregnant people are especially vulnerable to the health harms resulting from climate change, namely, preterm birth, small for gestational age, hypertensive disorders of pregnancy, and other adverse reproductive health and birth outcomes. Strategies to minimize these harms include mitigation and adaptation.

Conclusions and Relevance

Physicians are in a unique position to protect the health of pregnant persons and children by advocating for policy changes that address climate change and providing clinical recommendations for patients to protect themselves from the health impacts of climate hazards.

Prenatal exposure to long-term heat stress and stillbirth in Ghana: A within-space time-series analysis

INTRODUCTION

Few studies examined the association between prenatal long-term ambient temperature exposure and stillbirth and fewer still from developing countries. Rather than ambient temperature, we used a human thermophysiological index, Universal Thermal Climate Index (UTCI) to investigate the role of long-term heat stress exposure on stillbirth in Ghana.

METHODS

District-level monthly UTCI was linked with 90,532 stillbirths of 5,961,328 births across all 260 local districts between 1^st January 2012 and 31^st December 2020. A within-space time-series design was applied with distributed lag nonlinear models and conditional quasi-Poisson regression.

RESULTS

The mean (28.5 ± 2.1 °C) and median UTCI (28.8 °C) indicated moderate heat stress. The Relative Risks (RRs) and 95% Confidence Intervals (CIs) for exposure to lower-moderate heat (1st to 25th percentiles of UTCI) and strong heat (99th percentile) stresses showed lower risks, relative to the median UTCI. The higher-moderate heat stress exposures (75th and 90th percentiles) showed greater risks which increased with the duration of heat stress exposures and were stronger in the 90th percentile. The risk ranged from 2% (RR = 1.02, 95% CI 0.99, 1.05) to 18% (RR = 1.18, 95% CI 1.02, 1.36) for the 90th percentile, relative to the median UTCI. Assuming causality, 19 (95% CI 3, 37) and 27 (95% CI 3, 54) excess stillbirths per 10,000 births were attributable to long-term exposure to the 90th percentile relative to median UTCI for the past six and nine months, respectively. Districts with low population density, low gross domestic product, and low air pollution which collectively defined rural districts were at higher risk as compared to those in the high level (urban districts).

DISCUSSION

Maternal exposure to long-term heat stress was associated with a greater risk of stillbirth. Climate change-resilient interventional measures to reduce maternal exposure to heat stress, particularly in rural areas may help lower the risk of stillbirth.

Climate Change-Related Environmental Exposures and Perinatal and Maternal Health Outcomes in the U.S

PURPOSE

Climate change poses one of the greatest risks to human health as air pollution increases, surface temperatures rise, and extreme weather events become more frequent. Environmental exposures related to climate change have a disproportionate effect on pregnant women through influencing food and water security, civil conflicts, extreme weather events, and the spread of disease. Our research team sought to identify the current peer-reviewed research on the effects of climate change-related environmental exposures on perinatal and maternal health in the United States.

DESIGN AND METHODS

A systematic literature review of publications identified through a comprehensive search of the PubMed and Web of Science databases was conducted using a modified Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) approach. The initial search across both databases identified a combined total of 768 publications. We removed 126 duplicates and 1 quadruplet, and the remaining 639 publications were subjected to our pre-set inclusion and exclusion criteria. We excluded studies outside of the United States. A total of 39 studies met our inclusion criteria and were retained for thematic analysis.

FINDINGS

A total of 19 studies investigated the effect of either hot or cold temperature exposure on perinatal and maternal health outcomes. The effect of air pollution on perinatal outcomes was examined in five studies. A total of 19 studies evaluated the association between natural disasters (hurricanes, flash floods, and tropical cyclones) and perinatal and maternal health outcomes. High and low temperature extremes were found to negatively influence neonate and maternal health. Significant associations were found between air pollutant exposure and adverse pregnancy outcomes. Adverse pregnancy outcomes were linked to hurricanes, tropical cyclones, and flash floods.

CONCLUSIONS

This systematic review suggests that climate change-related environmental exposures, including extreme temperatures, air pollution, and natural disasters, are significantly associated with adverse perinatal and maternal health outcomes across the United States.

Prenatal acute thermophysiological stress and spontaneous preterm birth in Western Australia, 2000-2015: A space-time-stratified case-crossover analysis

Epidemiologic evidence on acute heat and cold stress and preterm birth (PTB) is inconsistent and based on ambient temperature rather than a thermophysiological index. The aim of this study was to use a spatiotemporal thermophysiological index (Universal Thermal Climate Index, UTCI) to investigate prenatal acute heat and cold stress exposures and spontaneous PTB. We conducted a space-time-stratified case-crossover analysis of 15,576 singleton live births with spontaneous PTB between January 1, 2000 and December 31, 2015 in Western Australia. The association between UTCI and spontaneous PTB was examined with distributed lag nonlinear models and conditional quasi-Poisson regression. Relative to the median UTCI, there was negligible evidence for associations at the lower range of exposures (1st to 25th percentiles). We found positive associations in the 95th and 99th percentiles, which increased with increasing days of heat stress in the first week of delivery. The relative risk (RR) and 95% confidence interval (CI) for the immediate (delivery day) and cumulative short-term (up to six preceding days) exposures to heat stress (99th percentile, 31.2 °C) relative to no thermal stress (median UTCI, 13.8 °C) were 1.01 (95% CI: 1.01, 1.02) and 1.05 (95% CI: 1.04, 1.06), respectively. Elevated effect estimates for heat stress were observed for the transition season, the year 2005-2009, male infants, women who smoked, unmarried, ≤ 19 years old, non-Caucasians, and high socioeconomic status. Effect estimates for cold stress (1st percentile, 0.7 °C) were highest in the transition season, during 2005-2009, and for married, non-Caucasian, and high socioeconomic status women. Acute heat stress was associated with an elevated risk of spontaneous PTB with sociodemographic vulnerability. Cold stress was associated with risk in a few vulnerable subgroups. Awareness and mitigation strategies such as hydration, reducing outdoor activities, affordable heating and cooling systems, and climate change governance may be beneficial. Further studies with the UTCI are required.

Maternal acute thermophysiological stress and stillbirth in Western Australia, 2000-2015: A space-time-stratified case-crossover analysis

BACKGROUND

The extreme thermal environment driven by climate change disrupts thermoregulation in pregnant women and may threaten the survival of the developing fetus.

OBJECTIVES

To investigate the acute effect of maternal exposure to thermophysiological stress (measured with Universal Thermal Climate Index, UTCI) on the risk of stillbirth and modification of this effect by sociodemographic disparities.

METHODS

We conducted a space-time-stratified case-crossover analysis of daily UTCI and 2835 singleton stillbirths between 1st January 2000 and 31st December 2015 across multiple small areas in Western Australia. Distributed lag non-linear models were combined with conditional quasi-Poisson regression to investigate the effects of the UTCI exposure from the preceding 6 days to the day of stillbirth. We also explored effect modification by fetal and maternal sociodemographic factors.

RESULTS

The median UTCI was 13.9 °C (representing no thermal stress) while the 1st and 99th percentiles were 0.7 °C (slight cold stress) and 31.7 °C (moderate heat stress), respectively. Relative to median UTCI, we found positive associations between acute maternal cold and heat stresses and higher risks of stillbirth, increasing with the intensity and duration of the thermal stress episodes. The cumulative risk from the preceding 6 days to the day of stillbirth was stronger in the 99th percentile (RR = 1.19, 95% CI: 1.17, 1.21) than the 1st percentile (RR = 1.14, 95% CI: 1.12, 1.15), relative to the median UTCI. The risks were disproportionately higher in term and male stillborn fetuses, smoking, unmarried, ≤19 years old, non-Caucasian, and low socioeconomic status mothers.

DISCUSSION

Acute maternal exposure to both cold and heat stresses may contribute to the risk of stillbirth and be exacerbated by sociodemographic disparities. The findings suggest public health attention, especially for the identified higher-risk groups. Future studies should consider the use of a human thermophysiological index, rather than surrogates such as ambient temperature.

Acute association between heatwaves and stillbirth in six US states

BACKGROUND

Heatwaves are becoming more frequent and may acutely increase the risk of stillbirth, a rare and severe pregnancy outcome.

OBJECTIVES

Examine the association between multiple heatwave metrics and stillbirth in six U.S. states.

METHODS

Data were collected from fetal death and birth records in California (1996-2017), Florida (1991-2017), Georgia (1994-2017), Kansas (1991-2017), New Jersey (1991-2015), and Oregon (1991-2017). Cases were matched to controls 1:4 based on maternal race/ethnicity, maternal education, and county, and exposure windows were aligned (gestational week prior to stillbirth). County-level temperature data were obtained from Daymet and linked to cases and controls by residential county and the exposure window. Five heatwave metrics (1 categorical, 3 dichotomous, 1 continuous) were created using different combinations of the duration and intensity of hot days (mean daily temperature exceeding the county-specific 97.5^th percentile) during the exposure window, as well as a continuous measure of mean temperature during the exposure window modeled using natural splines to allow for nonlinear associations. State-specific odds ratios (ORs) and 95% confidence intervals (CI) were estimated using conditional logistic regression models. State-specific results were pooled using a fixed-effects meta-analysis.

RESULTS

In our data set of 140,428 stillbirths (553,928 live birth controls), three of the five heatwave metrics examined were not associated with stillbirth. However, four consecutive hot days during the previous week was associated with a 3% increase in stillbirth risk (CI: 1.01, 1.06), and a 1 °C average increase over the threshold was associated with a 10% increase in stillbirth risk (CI: 1.04, 1.17). In continuous temperature analyses, there was a slight increased risk of stillbirth associated with extremely hot temperatures (≥ 35 °C).

DISCUSSION

Most heat wave definitions examined were not associated with acute changes in stillbirth risk; however, the most extreme heatwave durations and temperatures were associated with a modest increase in stillbirth risk.

Extreme Heat and Pregnancy Outcomes: A Scoping Review of the Epidemiological Evidence

Background: Extreme heat caused by climate change is a major public health concern, disproportionately affecting poor and racialized communities. Gestational heat exposure is a well-established teratogen in animal studies, with a growing body of literature suggesting human pregnancies are similarly at risk. Characterization of extreme heat as a pregnancy risk is problematic due to nonstandard definitions of heat waves, and variable study designs. To better focus future research in this area, we conducted a scoping review to assess the effects of extreme heat on pregnancy outcomes. Methods: A scoping review of epidemiological studies investigating gestational heat-exposure and published 2010 and 2020, was conducted with an emphasis on study design, gestational windows of sensitivity, adverse pregnancy outcomes and characterization of environmental temperatures. Results: A sample of 84 studies was identified, predominantly set in high-income countries. Preterm birth, birthweight, congenital anomalies and stillbirth were the most common pregnancy outcome variables. Studies reported race/ethnicity and/or socioeconomic variables, however these were not always emphasized in the analysis. Conclusion: Use of precise temperature data by most studies avoided pitfalls of imprecise, regional definitions of heat waves, however inconsistent study design, and exposure windows are a significant challenge to systematic evaluation of this literature. Despite the high risk of extreme heat events and limited mitigation strategies in the global south, there is a significant gap in the epidemiological literature from these regions. Greater consistency in study design and exposure windows would enhance the rigor of this field.

Effect of Elevated Ambient Temperature on Maternal, Foetal, and Neonatal Outcomes: A Scoping Review

This scoping review provides an overview of the published literature, identifies research gaps, and summarises the current evidence of the association between elevated ambient temperature exposure during pregnancy and adverse maternal, foetal, and neonatal outcomes. Following the PRISMA extension for scoping reviews reporting guidelines, a systematic search was conducted on CINAHL, PubMed, and Embase and included original articles published in the English language from 2015 to 2020 with no geographical limitations. A total of seventy-five studies were included, conducted across twenty-four countries, with a majority in the USA (n = 23) and China (n = 13). Study designs, temperature metrics, and exposure windows varied considerably across studies. Of the eighteen heat-associated adverse maternal, foetal, and neonatal outcomes identified, pre-term birth was the most common outcome (n = 30), followed by low birth weight (n = 11), stillbirth (n = 9), and gestational diabetes mellitus (n = 8). Overall, papers reported an increased risk with elevated temperature exposures. Less attention has been paid to relationships between heat and the diverse range of other adverse outcomes such as congenital anomalies and neonatal mortality. Further research on these less-reported outcomes is needed to improve understanding and the effect size of these relationships with elevated temperatures, which we know will be exacerbated by climate change.

Universal Thermal Climate Index (UTCI) and adverse pregnancy outcomes in Ahvaz, Iran

Background

Climate change may jeopardize the health of mothers and their offspring. There are few studies on the association between increasing temperature and pregnancy outcomes. The aim of this study was to investigate the relation between Universal Thermal Climate Index (UTCI) and adverse pregnancy outcomes including stillbirth, low birth weight (LBW), preterm labor (PTL), spontaneous abortion (SA), preeclampsia and hypertension in Ahvaz, Iran.

Methods

Distributed Lag Non-linear Models (DLNM) combined with quasi-Poisson regression were used to research the effect of UTCI on adverse pregnancy outcomes. The effect of time trend, air pollutants (NO₂, SO₂ and PM₁₀), and weekdays were adjusted.

Results

The results showed that the low values of UTCI index (11.6 °C, in lags 0–6, 0–13) caused significant increase in the risk of preterm labor. However, hot thermal stress (high UTCI) significantly increased the risk of stillbirth in lag 0–13. We did not observe any significant relation between UTCI and other pregnancy outcomes in this study.

Conclusions

It seems like both hot and cold weathers can be associated with adverse pregnancy outcomes.

Scientists have found that climate change has adverse effects on human health. Because pregnant women are one of the most vulnerable groups, these negative impacts may affect their fetuses, which make up the next generation. In this study, we examined the effect of temperature on some pregnancy outcomes, including low birth weight, preterm labor, spontaneous abortion, preeclampsia and gestational hypertension in Ahvaz city, which is one of the hottest cities in the world.

One way to assess temperature impact on humans is by using temperature indicators. In this study we used the Universal Thermal Climate Index (UTCI) for this purpose. The data at different time intervals were collected and evaluated with specific models.

Our results showed that low values of UTCI, which is equivalent to cold weather, significantly increase the risk of preterm labor. But, high levels of UTCI, which means hot weather, significantly increase the risk of stillbirth.

In conclusion; both hot and cold weather can be associated with adverse pregnancy outcomes in Ahvaz city. Therefore, pregnant women should protect themselves from exposure to hot and cold weather.

Extreme heat, preterm birth, and stillbirth: A global analysis across 14 lower-middle income countries

Stillbirths and complications from preterm birth are two of the leading causes of neonatal deaths across the globe. Lower- to middle-income countries (LMICs) are experiencing some of the highest rates of these adverse birth outcomes. Research has suggested that environmental determinants, such as extreme heat, can increase the risk of preterm birth and stillbirth. Under climate change, extreme heat events have become more severe and frequent and are occurring in differential seasonal patterns. Little is known about how extreme heat affects the risk of preterm birth and stillbirth in LMICs. Thus, it is imperative to examine how exposure to extreme heat affects adverse birth outcomes in regions with some of the highest rates of preterm and stillbirths. Most of the evidence linking extreme heat and adverse birth outcomes has been generated from high-income countries (HICs) notably because measuring temperature in LMICs has proven challenging due to the scarcity of ground monitors. The paucity of health data has been an additional obstacle to study this relationship in LMICs. In this study, globally gridded meteorological data was linked with spatially and temporally resolved Demographic and Health Surveys (DHS) data on adverse birth outcomes. A global analysis of 14 LMICs was conducted per a pooled time-stratified case-crossover design with distributed-lag nonlinear models to ascertain the relationship between acute exposure to extreme heat and PTB and stillbirths. We notably found that experiencing higher maximum temperatures and smaller diurnal temperature range during the last week before birth increased the risk of preterm birth and stillbirth. This study is the first global assessment of extreme heat events and adverse birth outcomes and builds the evidence base for LMICs.

Air pollution and preterm birth: A time-stratified case-crossover study in the San Joaquin Valley of California

BACKGROUND

Air pollution is linked to preterm birth (PTB), but existing studies are primarily focused on chronic exposures, conducted in areas with moderate pollution, and/or subject to confounding.

OBJECTIVES

We investigated short-term associations between two pollutants [particulate matter <2.5 microns (PM_2.5 ) and ozone] and PTB, and estimated excess PTB cases potentially attributed to these pollutants.

METHODS

This time-stratified case-crossover study includes 196,970 singleton pregnancies affected by PTB and early term birth from the San Joaquin Valley (SJV), California, USA (2007-2015). Daily ozone and PM_2.5 concentrations were estimated by the SJV Air Pollution Control District and geospatially linked to maternal zip code. We used conditional logistic regression models to estimate the odds ratio (OR) and 95% confidence intervals (CI) for the associations between an interquartile range (IQR) increase in pollutants and very preterm (VPTB, 20-34 weeks), moderate preterm (MPTB, 34-36 weeks) and early term births (ETB, 37-38 weeks). We adjusted all models for co-pollutants and meteorological factors.

RESULTS

During warm seasons (May-October), an IQR increase in ozone was associated with 9-11% increased odds of VPTB from lag 0 (OR_lag0 1.09, 95% CI 1.04,1.16) to lag 7 (OR_lag7 1.11, 95% CI 1.04,1.16). Findings were consistent for MPTB and ETB. Ozone was potentially responsible for an excess of 3-6 VPTBs, 7-9 PTBs and 24-42 ETBs per 1,000 singleton deliveries. During cold seasons (November-April), increased PM_2.5 exposure was associated with 5-6% increased odds of VPTB beginning at lag 3 (OR_lag3 1.06, 95% CI 1.02,1.11). PM_2.5 was associated with an excess of 1-3 VPTBs, 0-3 MPTBs and 6-18 ETBs per 1,000 singleton deliveries.

CONCLUSIONS

PM_2.5 and ozone are associated with increased risk of VPTB, MPTB and ETB within one week of exposure and are potential contributors to the increasing PTB trend. More research is needed to further understand the role of air pollution on PTB risk.

Ambient temperature and stillbirth risks in northern Sweden, 1880-1950

Background

Climate vulnerability of the unborn can contribute to adverse birth outcomes, in particular, but it is still not well understood. We investigated the association between ambient temperature and stillbirth risk among a historical population in northern Sweden (1880-1950).

Methods

We used digitized parish records and daily temperature data from the study region covering coastal and inland communities some 600 km north of Stockholm, Sweden. The data included 141,880 births, and 3,217 stillbirths, corresponding to a stillbirth rate of 22.7 (1880-1950). The association between lagged temperature (0-7 days before birth) and stillbirths was estimated using a time-stratified case-crossover design. Incidence risk ratios (IRR) with 95% confidence intervals were computed, and stratified by season and sex.

Results

We observed that the stillbirth risk increased both at low and high temperatures during the extended summer season (April to September), at -10°C, and the IRR was 2.3 (CI 1.28, 4.00) compared to the minimum mortality temperature of +15°C. No clear effect of temperature during the extended winter season (October to March) was found. Climate vulnerability was greater among the male fetus compared to the female counterparts.

Conclusion

In this subarctic setting before and during industrialization, both heat and cold during the warmer season increased the stillbirth risk. Urbanization and socio-economic development might have contributed to an uneven decline in climate vulnerability of the unborn.

The effects of desert dust storms, air pollution, and temperature on morbidity due to spontaneous abortions and toxemia of pregnancy: 5-year analysis

Epidemiological studies have suggested an association between particulate air pollution, increased temperatures, and morbidity related to pregnancy outcomes. However, the roles of desert dust storms and climatological factors have not been fully addressed. The objectives of the present study were to investigate the association between desert dust storms, particulate matter with a diameter ≤10 μm (PM₁₀), daily temperatures, and toxemia of pregnancy and spontaneous abortion in Gaziantep, South East Turkey. The study was conducted retrospectively at emergency department of two hospitals in Gaziantep city. Data from January 1, 2009, to March 31, 2014, were collected. Patients, who were diagnosed with toxemia of pregnancy and spontaneous abortion by radiological imaging modalities, were included in the study. Daily temperature ranges, mean temperature values, humidity, pressure, wind speed, daily PM10 levels, and records of dust storms were collected. A generalized additive regression model was designed to assess variable effects on toxemia of pregnancy and spontaneous abortion, while adjusting for possible confounding factors. Our findings demonstrated that presence of dust storms was positively associated with the toxemia of pregnancy both in outpatient admissions (OR=1.543 95% CI=1.186-2.009) and inpatient hospitalizations (OR=1.534; 95% CI=1.162-2.027). However, neither PM₁₀ nor maximum temperature showed a marked association with spontaneous abortion or toxemia of pregnancy in our study population. Our findings suggest that desert dust storms may have an impact on the risk for adverse pregnancy outcomes such as toxemia of pregnancy. Health authorities should take necessary measures to protect pregnant women against detrimental effects of these storms.

Ambient heat and stillbirth in Northern and Central Florida

BACKGROUND

Elevated temperature is well-recognized as a health hazard, and may be particularly harmful to pregnant women, including increasing risk of stillbirth. We conducted a study in Northern and Central Florida, an area prone to periodic extreme heat but with significant seasonal variation, focusing on the most socioeconomically vulnerable populations least able to mitigate the impact of heat.

METHODS

We obtained electronic health records data from the OneFlorida Data Trust for the period 2012-2017, with 1876 stillbirths included in the analysis. We used a case-crossover design to examine the risk of stillbirth associated with acute exposures to elevated heat prior to the outcome, contrasting the case period (the week preceding the stillbirth) with a control period (the week prior to the case period and the week after the stillbirth). Average heat index and maximum warning level during the case and control periods of each woman were assigned by ZIP code. Conditional logistic regression models were used to assess the association between stillbirth and heat exposure, controlling for PM_2.5 and O₃.

RESULTS

The adjusted odds ratio showed no overall association with stillbirth except for a weak association for exposure above the 90th percentile which was larger among the most socioeconomically deprived and non-Hispanic Black women. In the hot months, there was a clear association for all indices of heat exposure, but largest again for the most socioeconomically deprived population (aOR = 2.4, 95% CI: 1.2-5.2 in the 4th vs. 1st quartile) and among non-Hispanic Black women (aOR = 1.8, 95% CI: 1.0-3.2 in the 4th vs. 1st quartile).

CONCLUSIONS

Our results provide further evidence that elevated ambient heat is related to stillbirth and encourage a focus on the most susceptible individuals and possible clinical pathways.

Association between Physiological Equivalent Temperature (PET) with adverse pregnancy outcomes in Ahvaz, southwest of Iran

Background

There are few epidemiological studies on the relation between temperature changes and adverse pregnancy outcomes. The purpose of this study was to determine the relation between Physiological Equivalent Temperature (PET) with adverse pregnancy outcomes including stillbirth, low birth weight (LBW), preterm labor (PTL), spontaneous abortion (SA), preeclampsia and hypertension in Ahvaz, Iran.

Methods

Distributed Lag Non-linear Models (DLNM) combined with quasi-Poisson regression were used to investigate the effect of PET on adverse pregnancy outcomes. In this study the effect of time trend, air pollutants (NO₂, SO₂ and PM₁₀), and weekdays were adjusted.

Results

High PET (45.4 C°, lag = 0) caused a significant increase in risk of stillbirth. Also, high levels of PET (45.4, 43.6, 42.5 C°, lag = 0–6) and low levels of PET (9.9, 16.9 C°, lags = 0, 0–13, 0–21) significantly increased the risk of LBW. But, low levels of PET (6.4, 9.9, 16.9 C°, lags = 0–6, 0–13) reduced the risk of gestational hypertension.

Conclusion

The results of this study showed that hot and cold thermal stress may be associated with increased risk of stillbirth, and LBW in Ahvaz.

Systematic review of ambient temperature exposure during pregnancy and stillbirth: Methods and evidence

BACKGROUND

Associations between ambient temperature exposure during pregnancy and stillbirth have been reviewed and described in the literature. However, there is no existing review of environmental and epidemiologic methods applied to measure stillbirths resulting from exposure to ambient temperatures during pregnancy. The objective of this study is to systematically review published methods, data sources, and data linkage practices to characterize associations between ambient temperature and stillbirth to inform stillbirth prevention and risk management strategies.

METHODS

A systematic review of published studies that assess the association between ambient temperature exposure during pregnancy using any measures or approach and stillbirth was undertaken in Cochrane Library, PubMed, Medline, Scopus, Embase, and Web of Science of studies (2000-2020, inclusive). Selection of studies were assessed by pre-specified eligibility criteria and documented using PRISMA. Citations were managed using EndNote X8 whilst selection, reviewing, and data extraction were performed using Covidence. The screening, selection, and data extraction process consisted of two blind, independent reviews followed by a tertiary independent review. An adapted Critical Appraisal Skills Program (CASP) checklist was used to assess quality and bias. The main findings and characteristics of all studies was extracted and summarized. Where appropriate, a meta-analysis will be performed for measures of association.

RESULTS

Among 538 original records, 12 eligible articles were identified that analysed associations between ambient temperature exposure and stillbirth for 42,848 stillbirths among 3.4 million births across seven countries. Varied definitions of stillbirth were reported based on gestational age, birthweight, both, or neither. The overall rate of stillbirth ranged from 1.9 to 38.4 per 1000 among six high-income countries and one low-middle-income country. All study designs were retrospective and included ten cohort studies, three case-crossover studies, and two additional case-control subgroup analysis. Exposure data for ambient temperature was mostly derived from standard municipal or country-level monitors based on weather stations (66.6%) or a forecasting model (16.7%); otherwise, not reported (16.7%). Results were not statistically pooled for a meta-analysis due to heterogeneity of methods and models among included studies. All studies reported associations of increased risk of stillbirth with ambient temperature exposures throughout pregnancy, particularly in late pregnancy. One study estimates 17-19% (PAR) of stillbirths are potentially attributable to chronic exposure to hot and cold ambient temperatures during pregnancy. Overall, risk of stillbirth was observed to increase below 15 °C and above 23.4 °C, where highest risk is above 29.4 °C.

CONCLUSION

Exposure to hot and cold temperatures during pregnancy may increase the risk of stillbirth, although a clear causative mechanism remains unknown. Despite lack of causal evidence, existing evidence across diverse settings observed similar effects of increased risk of stillbirth using a variety of statistical and methodological approaches for exposure assessments, exposure windows, and data linkage. Managing exposure to ambient temperatures during pregnancy could potentially decrease risk of stillbirth, particularly among women in low-resource settings where access to safe antenatal and obstetric care is challenging. To fully understand the effects or dose-response relationship of maternal exposure to ambient temperatures and stillbirth, future studies should focus on biological mechanisms and contributing factors in addition to improving measurement of ambient temperature exposure.

Exploring Strategies for Investigating the Mechanisms Linking Climate and Individual-Level Child Health Outcomes: An Analysis of Birth Weight in Mali

The goal of this article is to consider data solutions to investigate the differential pathways that connect climate/weather variability to child health outcomes. We apply several measures capturing different aspects of climate/weather variability to different time periods of in utero exposure. The measures are designed to capture the complexities of climate-related risks and isolate their impacts based on the timing and duration of exposure. Specifically, we focus on infant birth weight in Mali and consider local weather and environmental conditions associated with the three most frequently posited potential drivers of adverse health outcomes: disease (malaria), heat stress, and food insecurity. We focus this study on Mali, where seasonal trends facilitate the use of measures specifically designed to capture distinct aspects of climate/weather conditions relevant to the potential drivers. Results indicate that attention to the timing of exposures and employing measures designed to capture nuances in each of the drivers provides important insight into climate and birth weight outcomes, especially in the case of factors impacted by precipitation. Results also indicate that high temperatures and low levels of agricultural production are consistently associated with lower birth weights, and exposure to malarious conditions may increase likelihood of nonlive birth outcomes.

Post-conception heat exposure increases clinically unobserved pregnancy losses

Evidence of the relationship between temperature during pregnancy and human embryo mortality is limited. Most importantly, the literature lacks causal estimations and studies on early pregnancy losses. Here, we estimate the impact of early pregnancy temperature exposure on the clinically unobserved pregnancy loss rate. We use administrative data of clinically observed pregnancies from more than three decades for Hungary. We apply an empirical approach that allows us to infer the impact of temperature on the clinically unobserved pregnancy loss rate from the estimated effects on the clinically observed conception rate. The results show that exposure to hot temperatures during the first few weeks after the conception week increases the clinically unobserved pregnancy loss rate, whereas exposure to colder temperatures seems to decrease it. Importantly, the temperature-induced changes represent changes in the total number of pregnancy losses rather than a compositional change between clinically observed and clinically unobserved pregnancy losses.

A case-crossover study of short-term air pollution exposure and the risk of stillbirth in California, 1999-2009

BACKGROUND

Associations between ambient air pollution and stillbirth have recently been explored, but most studies have focused on long-term (trimester or gestational averages) rather than short-term (within one week) air pollution exposures.

OBJECTIVE

To evaluate whether short-term exposures to criteria air pollutants are associated with increased risk of stillbirth.

METHODS

Using air pollution and fetal death certificate data from 1999 to 2009, we assessed associations between acute prenatal air pollution exposure and stillbirth in California. In a time-stratified case-crossover study, we analyzed single day and/or cumulative average days (up to a 6 day lag) of exposure to fine (PM_2.5) and coarse particles (PM_10-2.5), ozone (O₃), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), and carbon monoxide (CO) for mothers estimated to reside within 10 km of a pollution monitor based on reported zip code. We also examined potential confounding by apparent temperature or co-pollutants, and effect modification by maternal demographic factors, fetal sex, gestational age, and cause of stillbirth.

RESULTS

Stillbirth cases in the primary analyses ranged between 1,203 and 13,018, depending on the pollutant. For an IQR increase in SO₂ (lag 4), O₃ (lag 4), and PM_10-2.5 (lag 2), we found a 2.8% (95% confidence interval (CI) 0.2%, 5.5%), 5.8% (95% CI 1.6%, 10.1%), and 6.1% (95% CI 0.1%, 12.4%) increase in the odds of stillbirth, respectively. Additional adjustment by apparent temperature had little effect on the SO₂ association but slightly attenuated O₃ (adjusted % change: 4.2% (95% CI -0.2%, 8.9%) and PM_10-2.5 (5.7% (95% CI -1.1%, 13.0%)) associations, while other co-pollutants had minimal impact. Associations were observed specifically for stillbirths from obstetric complications and in women with higher educational attainment.

CONCLUSIONS

This study provides evidence for associations between prenatal short-term air pollution exposure, specifically SO₂, O_3, and PM_10-2.5, and stillbirth in California and warrants replication of findings in other settings.

Effect of ambient air pollution and temperature on the risk of stillbirth: a distributed lag nonlinear time series analysis

OBJECTIVES

This study aimed to determine the effect of ambient air pollution and temperature on stillbirth in Tehran.

METHODS

In this time-series study, the effect of O3 (ppb), CO (ppm), NO2 (ppb), SO2 (ppb), PM2.5 (μg/m3), and minimum, maximum, and mean daily temperature (°C) on stillbirth was evaluated in Tehran, Iran between March 2015 and March 2018. Using a quasi-Poisson regression model in combination with a Distributed Lag Non-linear Models (DLNM), the Relative Risk (RR) was estimated through comparing the high temperature (99th, 95th, and 75th percentiles) and low temperature (1st, 5th, and 25th percentiles) with the median. The effect of air pollution was estimated for each 1-, 5-, or 10-unit increase in the concentration during lags (days) 0-21.

RESULTS

Among air pollutants, only a 5-ppm increase in the SO2 concentration in lag 0 increased the risk of stillbirth significantly (RR = 1.062; 1.002-1.125). The largest effect of heat was observed while comparing the 99th percentile of minimum daily temperature (26.9 °C) with the median temperature (13.2 °C), which was not statistically significant (RR = 1.25; 0.95-1.65). As for cold, a non-significant protective effect was observed while comparing the 1st percentile of maximum daily temperature (3.1 °C) with the median temperature (23.2 °C) (RR = 0.92; 0.72-1.19).

CONCLUSION

Each 5-ppm increase in the mean daily SO2 in lag 0 increased the risk of stillbirth by 6% while other air pollutants had no significant effects on stillbirth. In lags 0 and 1, the heat increased the risk of stillbirth while the cold had protective effects, which were not statistically significant.

Associations between high temperatures in pregnancy and risk of preterm birth, low birth weight, and stillbirths: systematic review and meta-analysis

OBJECTIVE

To assess whether exposure to high temperatures in pregnancy is associated with increased risk for preterm birth, low birth weight, and stillbirth.

DESIGN

Systematic review and random effects meta-analysis.

DATA SOURCES

Medline and Web of Science searched up to September 2018, updated in August 2019.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Clinical studies on associations between high environmental temperatures, and preterm birth, birth weight, and stillbirths.

RESULTS

14 880 records and 175 full text articles were screened. 70 studies were included, set in 27 countries, seven of which were countries with low or middle income. In 40 of 47 studies, preterm births were more common at higher than lower temperatures. Exposures were classified as heatwaves, 1°C increments, and temperature threshold cutoff points. In random effects meta-analysis, odds of a preterm birth rose 1.05-fold (95% confidence interval 1.03 to 1.07) per 1°C increase in temperature and 1.16-fold (1.10 to 1.23) during heatwaves. Higher temperature was associated with reduced birth weight in 18 of 28 studies, with considerable statistical heterogeneity. Eight studies on stillbirths all showed associations between temperature and stillbirth, with stillbirths increasing 1.05-fold (1.01 to 1.08) per 1°C rise in temperature. Associations between temperature and outcomes were largest among women in lower socioeconomic groups and at age extremes. The multiple temperature metrics and lag analyses limited comparison between studies and settings.

CONCLUSIONS

Although summary effect sizes are relatively small, heat exposures are common and the outcomes are important determinants of population health. Linkages between socioeconomic status and study outcomes suggest that risks might be largest in low and middle income countries. Temperature rises with global warming could have major implications for child health.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD 42019140136 and CRD 42018118113.

Ambient temperature and stillbirth: Risks associated with chronic extreme temperature and acute temperature change

BACKGROUND

Ambient temperature events are increasing in frequency and intensity. Our prior work in a U.S. nationwide study suggests a strong association between both chronic and acute temperature extremes and stillbirth risk.

OBJECTIVE

We attempted to replicate our prior study by assessing stillbirth risk associated with average whole-pregnancy temperatures and acute ambient temperature changes in a low-risk U.S.

METHODS

Singleton deliveries in the NICHD Consecutive Pregnancies Study (Utah, 2002-2010; n = 112,005) were identified using electronic medical records. Ambient temperature was derived from the Weather Research and Forecasting model. Binary logistic regression determined the adjusted odds ratio (aOR) and 95% confidence interval (95% CI) for stillbirth associated with whole-pregnancy exposure to extreme cold (<10th percentile) and hot (>90th percentile) versus moderate (10th-90th percentiles) average temperature, adjusting for maternal demographics, season of conception, hypertensive disorders of pregnancy, and gestational diabetes. In a case-crossover analysis, we estimated the stillbirth aOR and 95% CI for each 1° Celsius increase during the week prior to delivery using conditional logistic regression. In both models, we adjusted for relative humidity, ozone, and fine particulates.

RESULTS

We observed 500 stillbirth cases among 498 mothers. Compared to moderate temperatures, whole-pregnancy exposure to extreme cold (aOR: 4.42, 95% CI:3.43, 5.69) and hot (aOR: 5.06, 95% CI: 3.34, 7.68) temperatures were associated with stillbirth risk. Case-crossover models observed a 7% increased odds (95% CI: 1.04, 1.10) associated with each 1° Celsius increase during the week prior to delivery.

DISCUSSION

Both chronic and acute ambient temperature were associated with odds of stillbirth in this low-risk population, similar to our prior nationwide findings. Future increases in temperature extremes are likely and the observed risk in a low-risk population suggests this association merits attention.

Community-based maternal health workers' perspectives on heat risk and safety: a pilot qualitative study

In this study the authors examined how maternal health workers (MHWs) perceive the health risks of extreme heat exposure to pregnant women and fetuses. The authors conducted interviews with 12 MHWs (including midwives and doulas) in El Paso, Texas. Using qualitative analysis, the researchers identified numerous themes. Although heat was not communicated as a major health risk, participants expressed some concern with growing heat exposure and communicated standard protective measures. While all participants were familiar with some heat illness symptoms, they were generally unaware of their clients' vulnerability. MHWs' minimal heat-risk knowledge leaves pregnant women and developing fetuses at risk of preventable harm.

Association between ambient temperature and hypertensive disorders in pregnancy in China

Hypertensive disorders in pregnancy (HDPs) are leading perinatal diseases. Using a national cohort of 2,043,182 pregnant women in China, we evaluated the association between ambient temperatures and HDP subgroups, including preeclampsia or eclampsia, gestational hypertension, and superimposed preeclampsia. Under extreme temperatures, very cold exposure during preconception (12 weeks) increases odds of preeclampsia or eclampsia and gestational hypertension. Compared to preconception, in the first half of pregnancy, the impact of temperature on preeclampsia or eclampsia and gestational hypertension is opposite. Cold exposure decreases the odds, whereas hot exposure increases the odds. Under average temperatures, a temperature increase during preconception decreases the risk of preeclampsia or eclampsia and gestational hypertension. However, in the first half of pregnancy, temperature is positively associated with a higher risk. No significant association is observed between temperature and superimposed preeclampsia. Here we report a close relationship exists between ambient temperature and preeclampsia or eclampsia and gestational hypertension.

Hypertensive disorders in pregnancy are prevalent perinatal diseases. Here the authors report an association between ambient temperature before or after conception and risk of preeclampsia or eclampsia and gestational hypertension.

Associations of maternal ambient temperature exposures during pregnancy with the placental weight, volume and PFR: A birth cohort study in Guangzhou, China

BACKGROUND

The placenta performs crucial functions to ensure normal fetal development. Experimental studies have indicated associations between exposure to elevated temperatures during pregnancy and reduction in placental weight and volume. However, epidemiological studies in humans are lacking.

OBJECTIVE

To estimate the associations between prenatal exposure to ambient temperature with placental weight, volume, and the placental weight to birth weight ratio (PFR).

METHODS

We conducted a prospective birth cohort study using the Prenatal Environment and Offspring Health Cohort (PEOH Cohort) beginning in 2016 in Guangzhou, China. Women in early pregnancy were recruited and followed up during their hospitalization for childbirth. An inverse distance-weighted method was employed to estimate the average temperature exposure of every 4 weeks as well as the trimester-specific average temperature exposure at the individual's residential address. A generalized linear model was applied to estimate the effects of temperature exposure during pregnancy on the placental weight, volume, and PFR.

RESULTS

A total of 4051 pregnant women were enrolled. Compared with the reference temperature of 20 °C, maternal exposure to 29 °C (95th centile) during late pregnancy was associated with an average of -6.03 g (95% confidence interval [CI]: -11.28 g, -0.78 g) in placental weight, -16.15 cm³ (95% CI: -26.24 cm³, -6.07 cm³) in placental volume, and 0.26 (95% CI: 0.07, 0.45) in PFR. The peak effects of high temperatures on placental weight, volume, and PFR were found from 29 to 32 weeks (β = -3.79 g, 95% CI: -8.39 g, 0.82 g), 37 to 40 weeks (β = -19.34 cm³, 95% CI: -30.99 cm³, -7.69 cm³), and 25 to 28 weeks (β = 0.35, 95% CI: 0.04, 0.66), respectively.

CONCLUSIONS

Maternal exposure to elevated temperatures was associated with a decrease in placental weight and volume and an increase in PFR. The associations were stronger when exposures occurred during late pregnancy.

Association of Air Pollution and Heat Exposure With Preterm Birth, Low Birth Weight, and Stillbirth in the US: A Systematic Review

IMPORTANCE

Knowledge of whether serious adverse pregnancy outcomes are associated with increasingly widespread effects of climate change in the US would be crucial for the obstetrical medical community and for women and families across the country.

OBJECTIVE

To investigate prenatal exposure to fine particulate matter (PM2.5), ozone, and heat, and the association of these factors with preterm birth, low birth weight, and stillbirth.

EVIDENCE REVIEW

This systematic review involved a comprehensive search for primary literature in Cochrane Library, Cochrane Collaboration Registry of Controlled Trials, PubMed, ClinicalTrials.gov website, and MEDLINE. Qualifying primary research studies included human participants in US populations that were published in English between January 1, 2007, and April 30, 2019. Included articles analyzed the associations between air pollutants or heat and obstetrical outcomes. Comparative observational cohort studies and cross-sectional studies with comparators were included, without minimum sample size. Additional articles found through reference review were also considered. Articles analyzing other obstetrical outcomes, non-US populations, and reviews were excluded. Two reviewers independently determined study eligibility. The Arskey and O'Malley scoping review framework was used. Data extraction was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guideline.

FINDINGS

Of the 1851 articles identified, 68 met the inclusion criteria. Overall, 32 798 152 births were analyzed, with a mean (SD) of 565 485 (783 278) births per study. A total of 57 studies (48 of 58 [84%] on air pollutants; 9 of 10 [90%] on heat) showed a significant association of air pollutant and heat exposure with birth outcomes. Positive associations were found across all US geographic regions. Exposure to PM2.5 or ozone was associated with increased risk of preterm birth in 19 of 24 studies (79%) and low birth weight in 25 of 29 studies (86%). The subpopulations at highest risk were persons with asthma and minority groups, especially black mothers. Accurate comparisons of risk were limited by differences in study design, exposure measurement, population demographics, and seasonality.

CONCLUSIONS AND RELEVANCE

This review suggests that increasingly common environmental exposures exacerbated by climate change are significantly associated with serious adverse pregnancy outcomes across the US.

A protocol for an observational cohort study of heat strain and its effect on fetal wellbeing in pregnant farmers in The Gambia

Introduction: Climate change predictions indicate that global temperatures are likely to exceed those seen in the last 200,000 years, rising by around 4°C above pre-industrial levels by 2100 (without effective mitigation of current emission rates). In regions of the world set to experience extreme temperatures, women often work outside in agriculture even during pregnancy. The implications of heat strain in pregnancy on maternal health and pregnancy outcome are not well understood. This protocol describes a study to assess the physiological response of pregnant women to environmental heat stress and the immediate effect this has on fetal wellbeing.

Methods and analysis: The study will be performed in West Kiang district, The Gambia; a semi-arid zone in West Africa with daily maximum temperatures ranging from approximately 32 to 40°C. We will recruit 125 pregnant women of all ages who perform agricultural work during their pregnancy. Participants will be followed every two months until delivery. At each study visit fetal growth will be measured by ultrasound scan. During the course of their working day we will take the following measurements: continuous maternal physiological measurements (heart rate, respiratory rate, chest skin temperature and tri-axis accelerometer data); intermittent maternal tympanic core temperature, four point skin temperature, blood pressure; intermittent fetal heart rate and, if eligible, umbilical artery doppler; intermittent environmental measurements of air temperature, humidity, solar radiation and wind speed. Venous blood and urine will be collected at beginning and end of day for biomarkers of heat strain or fetal distress and hydration status.

A protocol for an observational cohort study of heat strain and its effect on fetal wellbeing in pregnant farmers in The Gambia

Introduction: Climate change predictions indicate that global temperatures are likely to exceed those seen in the last 200,000 years, rising by around 4°C above pre-industrial levels by 2100 (without effective mitigation of current emission rates). In regions of the world set to experience extreme temperatures, women often work outside in agriculture even during pregnancy. The implications of heat strain in pregnancy on maternal health and pregnancy outcome are not well understood. This protocol describes a study to assess the physiological response of pregnant women to environmental heat stress and the immediate effect this has on fetal wellbeing. Methods and analysis: The study will be performed in West Kiang district, The Gambia; a semi-arid zone in West Africa with daily maximum temperatures ranging from approximately 32 to 40°C. We will recruit 125 pregnant women of all ages who perform agricultural work during their pregnancy. Participants will be followed every two months until delivery. At each study visit fetal growth will be measured by ultrasound scan. During the course of their working day we will take the following measurements: continuous maternal physiological measurements (heart rate, respiratory rate, chest skin temperature and tri-axis accelerometer data); intermittent maternal tympanic core temperature, four point skin temperature, blood pressure; intermittent fetal heart rate and, if eligible, umbilical artery doppler; intermittent environmental measurements of air temperature, humidity, solar radiation and wind speed. Venous blood and urine will be collected at beginning and end of day for biomarkers of heat strain or fetal distress and hydration status.

Building an interdisciplinary framework to advance conceptual and technical aspects of population-environment research focused on women's and children's health

Great gains have been made in providing researchers geo-spatial data that can be combined with population health data. This development is crucial given concerns over the human health outcomes associated with a changing climate. Merging population and environmental data remains both conceptually and technically challenging because of a large range of temporal and spatial scales. Here we propose a framework that addresses and advances both conceptual and technical aspects of population-environment research. This framework can be useful for considering how any time or space-based environmental occurrence influences population health outcomes and can be used to guide different data aggregation strategies. The primary consideration discussed here is how to properly model the space and time effects of environmental context on individual-level health outcomes, specifically maternal, child and reproductive health outcomes. The influx of geospatial health data and highly detailed environmental data, often at daily scales, provide an opportunity for population-environment researchers to move towards a more theoretically and analytically sound approach for studying environment and health linkages.

Associations of ambient temperature exposure during pregnancy with the risk of miscarriage and the modification effects of greenness in Guangdong, China

Miscarriage is one of the commonest complications of pregnancy. Although previous studies suggested that environmental factors were important causes of miscarriage, evidence is still inadequate. Here, we examined the association of maternal exposure to temperature with the risk of miscarriage and further assessed the modifying effects of surrounding residential greenness. A case-control study was conducted at a large hospital in Guangzhou, China. All participants' information was extracted from hospital records. An inverse distance weighted method was used to estimate the temperature exposure at each residential address, where the greenness was measured by Normalized Difference Vegetation Index (NDVI). A logistic regression model was applied to estimate the association of temperature exposure with the risk of miscarriage. A total of 2044 cases of miscarriage and 2285 controls were included in the present study. We observed a generally non-linear positive relationship between temperature exposure and the risk of miscarriage. More pronounced effects of high temperatures vs. low temperatures were found during the two months prior to hospitalization than in other periods. The odds ratio (OR) of 29.4 °C (95th centile) compared with 15 °C during the first month prior to hospitalization was 1.480 (95% CI: 1.021-2.145). Smaller effects of temperatures were seen on the risk of miscarriage among participants with moderately great surrounding greenness compared with those with less greenness. We concluded that maternal exposure to moderately high temperature during pregnancy may increase the risk of miscarriage, but the modifying effects of greenness on these associations need to be further tested in future studies.

Impacts of air pollution and noise on risk of preterm birth and stillbirth in London

BACKGROUND

Evidence for associations between ambient air pollution and preterm birth and stillbirth is inconsistent. Road traffic produces both air pollutants and noise, but few studies have examined these co-exposures together and none to date with all-cause or cause-specific stillbirths.

OBJECTIVES

To analyse the relationship between long-term exposure to air pollution and noise at address level during pregnancy and risk of preterm birth and stillbirth.

METHODS

The study population comprised 581,774 live and still births in the Greater London area, 2006-2010. Outcomes were preterm birth (<37 completed weeks gestation), all-cause stillbirth and cause-specific stillbirth. Exposures during pregnancy to particulate matter with diameter <2.5 μm (PM2.5) and <10 μm (PM10), ozone (O3), primary traffic air pollutants (nitrogen dioxide, nitrogen oxides, PM2.5 from traffic exhaust and traffic non-exhaust), and road traffic noise were estimated based on maternal address at birth.

RESULTS

An interquartile range increase in O3 exposure was associated with elevated risk of preterm birth (OR 1.15 95% CI: 1.11, 1.18, for both Trimester 1 and 2), all-cause stillbirth (Trimester 1 OR 1.17 95% CI: 1.07, 1.27; Trimester 2 OR 1.20 95% CI: 1.09, 1.32) and asphyxia-related stillbirth (Trimester 1 OR 1.22 95% CI: 1.01, 1.49). Odds ratios with the other air pollutant exposures examined were null or <1, except for primary traffic non-exhaust related PM2.5, which was associated with 3% increased odds of preterm birth (Trimester 1) and 7% increased odds stillbirth (Trimester 1 and 2) when adjusted for O3. Elevated risk of preterm birth was associated with increasing road traffic noise, but only after adjustment for certain air pollutant exposures.

DISCUSSION

Our findings suggest that exposure to higher levels of O3 and primary traffic non-exhaust related PM2.5 during pregnancy may increase risk of preterm birth and stillbirth; and a possible relationship between long-term traffic-related noise and risk of preterm birth. These findings extend and strengthen the evidence base for important public health impacts of ambient ozone, particulate matter and noise in early life.

Risk of particulate matter on birth outcomes in relation to maternal socio-economic factors: a systematic review

A growing number of studies provide evidence of an association between exposure to maternal air pollution during pregnancy and adverse birth outcomes including low birth weight and preterm birth. Prevention of these health effects of air pollution is critical to reducing the adverse infant outcomes, which can have impacts throughout the life course. However, there is no consensus on whether the association between air pollution exposure and birth outcomes varies by maternal risk factors including demographic characteristics and socio-economic status. Such information is vital to understand potential environmental health disparities. Our search found 859 unique studies, of which 45 studies met our inclusion criteria (Jan. 2000- July. 2019). We systematically reviewed the 45 identified epidemiologic studies and summarized the results on effect modifications by maternal race/ethnicity, educational attainment, income, and area-level socio-economic status. We considered adverse birth outcomes of preterm birth, low birth weight, small for gestational age (SGA), and stillbirth. Suggestive evidence of higher risk of particulate matter in infants of African-American/black mothers than infants of other women was found for preterm birth and low birth weight. We found weak evidence that particulate matter risk was higher for infants of mothers with lower educational attainment for preterm birth and low birth weight. Due to the small study numbers, we were unable to conclude whether effect modification is present for income, occupation, and area-level socio-economic status, and additional research is needed. Furthermore, adverse birth outcomes such as SGA and stillbirth need more study to understand potential environmental justice issues regarding the impact of particulate matter exposure during pregnancy on birth outcomes.

Weather extremes and perinatal mortality - Seasonal and ethnic differences in northern Sweden, 1800-1895

BACKGROUND

Many studies have shown the impact of heat and cold on total and age-specific mortality, but knowledge gaps remain regarding weather vulnerability of very young infants. This study assessed the association of temperature extremes with perinatal mortality (stillbirths and deaths in the first week of life), among two ethnic groups in pre-industrial northern Sweden.

METHODS

We used population data of indigenous Sami and non-Sami in selected parishes of northern Sweden, 1800-1895, and monthly temperature data. Multiple logistic regression models were conducted to estimate the association of cold (<10th percentile of temperature) and warmth (>90th percentile) in the month of birth with perinatal mortality, adjusted for cold and warmth in the month prior birth and period, stratified by season and ethnicity.

RESULTS

Perinatal mortality was slightly higher in Sami than in non-Sami (46 vs. 42 / 1000 live and stillbirths), but showed large variations across the region and over time. Both groups saw the highest perinatal mortality in autumn. For Sami, winter was a high-risk time as well, while for non-Sami, seasonality was less distinct. We found an association between exposure to cold and perinatal mortality among winter-born Sami [Odds ratio (OR) 1.91, 95% confidence interval (CI) 1.26-2.92, compared to moderate temperature], while there was little effect of cold or warmth during other seasons. Non-Sami, meanwhile, were affected in summer by warmth (OR 0.20, CI 0.05-0.81), and in autumn by cold (OR 0.39, CI 0.19-0.82).

CONCLUSIONS

In this pre-industrial, subarctic setting, the indigenous Sami's perinatal mortality was influenced by extreme cold in winter, while non-Sami seemed to benefit from high temperature in summer and low temperature in autumn. Climate vulnerability of these two ethnic groups sharing the same environment was shaped by their specific lifestyles and living conditions.

Temperature, placental abruption and stillbirth

BACKGROUND

Pregnant women may be vulnerable to changes in ambient temperature and warming climates. Recent evidence suggests that temperature increases are associated with placental abruption, a risk factor for stillbirth.

OBJECTIVES

We investigated the effect of acute exposures to apparent temperature on stillbirths in Harris County, Texas, 2008-2013.

METHODS

We conducted a case-crossover study to investigate the association between temperature and stillbirth among 708 women. We used data from the National Climatic Data Center to estimate maternal exposure to daily average apparent temperature over the days (lag days 1 through 6) preceding the stillbirth event. We employed symmetric bidirectional sampling to select six control periods one to three weeks before and after each event and applied conditional logistic regression to examine associations between increases of apparent temperature and stillbirths during the warm season (May-September). We adjusted for fine particulate matter (PM2.5), nitrogen dioxide (NO2) and ozone (O3) and used stratified analysis to examine differences in risk by maternal race/ethnicity. We also examined the association among stillbirths with and without placental abruptions.

RESULTS

Independent of air pollutant exposures, a 10 °F increase in apparent temperature in the week preceding delivery (lag days 1 to 6) was positively associated with a 45% (adjusted OR = 1.45, 95% confidence interval (CI): 1.18, 1.77) increase in risk for stillbirth. Risks were elevated for stillbirths occurring in June through August, for Hispanic and non-Hispanic Black women, but not for non-Hispanic Whites. We also observed elevated risks associated with temperature increases in the few days preceding delivery among stillbirths caused by placental abruption, with the risk being highest on lag day 1 (OR = 1.93, 95% CI: 1.15, 3.23).

CONCLUSIONS

Independent of maternal ambient air pollutant exposure, we found evidence of an association between apparent temperature increases in the week preceding an event and risk of stillbirth. Risks for stillbirth varied by race/ethnicity. Further, in the first study to evaluate the impact of temperature on a specific complication during pregnancy, the risks were higher among mothers with placental abruption.

Climate Shocks Constrain Human Fertility in Indonesia

Climate change is likely to induce a large range of household- and individual-level responses, including changes in human fertility behaviors and outcomes. These responses may have important implications for human and economic development and women's empowerment. Drawing on the literature linking climate conditions to rice cultivation in Indonesia, we use longitudinal household survey and high-resolution climate data to explore changes in childbearing intentions, family planning use, and births following community-level climate shocks from 1993 to 2015. We find that fertility intentions increase and family planning use declines in response to delays in monsoon onset occurring within the previous year, particularly for wealthier populations. However, women on farms are significantly more likely to use family planning and less likely to give birth following abnormally high temperatures during the previous five years. We also measure parallel shifts in household well-being as measured by rice, food, and non-food consumption expenditures. Our findings advance the environmental fertility literature by showing that longer duration environmental shocks can have impacts on fertility behaviors and outcomes. Collectively, our results illustrate human fertility responses to climate change in a country vulnerable to its effects, and demonstrate that in some cases, climate shocks can constrain human fertility.

Assessing the magnitude and uncertainties of the burden of selected diseases attributable to extreme heat and extreme precipitation under a climate change scenario in Michigan for the period 2041-2070

BACKGROUND

Extreme heat (EH) and extreme precipitation (EP) events are expected to increase with climate change in many parts of the world. Characterizing the potential future morbidity and mortality burden of EH and EP and associated costs, as well as uncertainties in the estimates, can identify areas for public health intervention and inform adaptation strategies. We demonstrate a burden of disease and uncertainty assessment using data from Michigan, USA, and provide approaches for deriving these estimates for locations lacking certain data inputs.

METHODS

Case-crossover analysis adapted from previous Michigan-specific modeling was used to characterize the historical EH-mortality relationship by county poverty rate and age group. Historical EH-associated hospitalization and emergency room visit risks from the literature were adapted to Michigan. In the U.S. Environmental Protection Agency's BenMAP software, we used a novel approach, with multiple spatially-varying exposures, to estimate all non-accidental mortality and morbidity occurring on EH days (EH days; days where maximum temperature 32.2-35 C or > 35 C) and EP days. We did so for two time periods: the "historical" period (1971-2000), and the "projected" period (2041-2070), by county.

RESULTS

The rate of all non-accidental mortality associated with EH days increased from 0.46/100,000 persons historically to 2.9/100,000 in the projected period, for 240 EH-attributable deaths annually. EH-associated ED visits increased from 12/100,000 persons to 68/100,000 persons, for 7800 EH-attributable emergency department visits. EP-associated ED visits increased minimally from 1.7 to 1.9/100,000 persons. Mortality and morbidity were highest among those aged 65+ (91% of all deaths). Projected health costs are dominated by EH-associated mortality ($280 million) and EH-associated emergency department visits ($14 million). A variety of sources contribute to a moderate-to-high degree of uncertainty around the point estimates, including uncertainty in the magnitude of climate change, population composition, baseline health rates, and exposure-response estimates.

CONCLUSIONS

The approach applied here showed that health burden due to climate may significantly rise for all Michigan counties by midcentury. The costs to health care and uncertainties in the estimates, given the potential for substantial attributable burden, provide additional information to guide adaptation measures for EH and EP.

Ambient air pollution and the risk of stillbirth: a population-based prospective birth cohort study in the coastal area of China

Accumulating evidence has shown that prenatal ambient air pollution exposure is associated with elevated stillbirth risk; however, the results are inconsistent. This population-based prospective cohort study aimed to explore the association between prenatal air pollution exposure and stillbirth rate in the coastal area in China. Data of air pollution and birth outcomes between January 1, 2015, and December 31, 2017, were collected. Among the 59,868 eligible births, there were 587 stillbirths and 59,281 live births. Although the air quality in this study was relatively better than most of the major cities in China, a positive association was still found between prenatal air pollution exposure and stillbirth rate. Every 10 μg/m³ increase of fine particulate matters (PM_2.5) in each trimester, as well as in the entire pregnancy, was associated with increased stillbirth rate (RR = 1.14, 1.11, 1.15, and 1.14 for the first, second, third trimester, and entire pregnancy, respectively). In addition, every 10 μg/m³ increase of PM₁₀ in the first trimester (RR = 1.09, 95% CI: 1.04-1.14), and 10 μg/m³ increase of O₃ in the first (RR = 1.05, 95% CI: 1.01-1.09) and third (RR = 1.04, 95% CI: 1.00-1.08) trimesters was also associated with increased stillbirth rate. The effects of PM_2.5 on stillbirth rate were found to be robust in the two-pollutant models. The findings of this study especially underscored the adverse effects of prenatal exposure of high levels of PM_2.5 on stillbirth. More studies are needed to verify our findings and further investigate the underlying mechanisms.

Temperature and Term Low Birth Weight in California

Few investigations have explored temperature and birth outcomes. In a retrospective cohort study, we examined apparent temperature, a combination of temperature and relative humidity, and term low birth weight (LBW) among 43,629 full-term LBW infants and 2,032,601 normal-weight infants in California (1999-2013). The California Department of Public Health provided birth certificate data, while meteorological data came from the California Irrigation Management Information System, US Environmental Protection Agency, and National Centers for Environmental Information. After considering several temperature metrics, we observed the best model fit for term LBW over the full gestation (per 10-degrees-Fahrenheit (°F) increase in apparent temperature, 13.0% change, 95% confidence interval: 4.1, 22.7) above 55°F, and the greatest association was for third-trimester exposure above 60°F (15.8%, 95% confidence interval: 5.0, 27.6). Apparent temperature during the first month of pregnancy exhibited no significant risk, while the first trimester had a significantly negative association, and second trimester, last month, and last 2 weeks had slightly increased risks. Mothers who were black or older, delivered male infants, or gave birth during the warm season had infants at the highest risks. This study provides further evidence for adverse birth outcomes from heat exposure for vulnerable subgroups of pregnant women.

Climate Change and Women's Health: Impacts and Opportunities in India

Climate change impacts on health, including increased exposures to heat, poor air quality, extreme weather events, and altered vector-borne disease transmission, reduced water quality, and decreased food security, affect men and women differently due to biologic, socioeconomic, and cultural factors. In India, where rapid environmental changes are taking place, climate change threatens to widen existing gender-based health disparities. Integration of a gendered perspective into existing climate, development, and disaster-risk reduction policy frameworks can decrease negative health outcomes. Modifying climate risks requires multisector coordination, improvement in data acquisition, monitoring of gender specific targets, and equitable stakeholder engagement. Empowering women as agents of social change can improve mitigation and adaptation policy interventions.

Selection in utero and population health: Theory and typology of research

Public health researchers may assume, based on the fetal origins literature, that "scarring" of birth cohorts describes the population response to modern-day stressors. We contend, based on extensive literature concerned with selection in utero, that this assumption remains questionable. At least a third and likely many more of human conceptions fail to yield a live birth. Those that survive to birth, moreover, do not represent their conception cohort. Increasing data availability has led to an improved understanding of selection in utero and its implications for population health. The literature describing selection in utero, however, receives relatively little attention from social scientists. We aim to draw attention to the rich theoretical and empirical literature on selection in utero by offering a typology that organizes this diverse work along dimensions we think important, if not familiar, to those studying population health. We further use the typology to identify important gaps in the literature. This work should interest social scientists for two reasons. First, phenomena of broad scholarly interest (i.e., social connectivity, bereavement) affect the extent and timing of selection in utero. Second, the life-course health of a cohort depends in part on the strength of such selection. We conclude by identifying new research directions and with a reconciliation of the apparent contradiction between the "fetal origins" literature and that describing selection in utero.