Trends, seasonality and effect of ambient temperature on preterm delivery

Exploring the mystical relationship between the Moon, Sun, and birth rate

OBJECTIVE

The Moon has a noticeable influence on the Earth due to its gravity, the most visible manifestation of which are tides. We aimed to see if the Moon's daily cycle, like the Sun's, affects the prevalence and incidence of childbirth.

METHODS

In this retrospective cohort study, we examined all deliveries at the Academic Hospital of Udine between 2001 and 2019. All consecutive singleton pregnancies with spontaneous labor and vaginal delivery were included.

RESULTS

During the period, 13,349 singleton pregnancies with spontaneous labor and vaginal delivery were delivered in 6939 days. A significantly higher prevalence of deliveries was found with the Moon above the horizon (50.63% vs. 49.37%, p < 0.05). Moreover, during the day, there was a significantly higher prevalence of deliveries than during nighttime (53.74% vs. 45.79%, p < 0.05). Combining the Moon and Sun altitude, the majority of deliveries were registered when both were above the horizon (27.39% vs. 26.13%, 23.25%, or 23.24%, p < 0.05). These findings were confirmed in multivariate analysis after adjusting for parity, gestational age, or season. We found no correlation between birth and the Moon phase.

CONCLUSIONS

Our data support the interaction of the Moon and the Sun in determining the time of birth. More research is needed to understand these phenomena and improve our understanding of labor initiation mechanisms.

Machine learning-based risk factor analysis of necrotizing enterocolitis in very low birth weight infants

This study used machine learning and a national prospective cohort registry database to analyze the major risk factors of necrotizing enterocolitis (NEC) in very low birth weight (VLBW) infants, including environmental factors. The data consisted of 10,353 VLBW infants from the Korean Neonatal Network database from January 2013 to December 2017. The dependent variable was NEC. Seventy-four predictors, including ambient temperature and particulate matter, were included. An artificial neural network, decision tree, logistic regression, naïve Bayes, random forest, and support vector machine were used to evaluate the major predictors of NEC. Among the six prediction models, logistic regression and random forest had the best performance (accuracy: 0.93 and 0.93, area under the receiver-operating-characteristic curve: 0.73 and 0.72, respectively). According to random forest variable importance, major predictors of NEC were birth weight, birth weight Z-score, maternal age, gestational age, average birth year temperature, birth year, minimum birth year temperature, maximum birth year temperature, sepsis, and male sex. To the best of our knowledge, the performance of random forest in this study was among the highest in this line of research. NEC is strongly associated with ambient birth year temperature, as well as maternal and neonatal predictors.

Effects of extreme temperature on the risk of preterm birth in China: A population-based multi-center cohort study

BACKGROUND

Extreme temperatures are associated with the risk of preterm birth (PTB), but evidence on the effects of different clinical subtypes and across different regions is limited. We aimed to evaluate the effects of maternal exposure to extreme temperature on PTB and its clinical subtypes in China, and to identify effect modification of regional factors in dimensions of population, economy, medical resources and environmental factors.

METHODS

This was a prospective population-based cohort of 210,798 singleton live births from 16 counties in eight provinces across China during 2014-2018. We used an extended Cox regression with time-varying variables to evaluate the effects of extreme heat and cold on PTB and its subtypes in the entire pregnancy, each trimester, the last gestational month and week. Meta-analysis and meta-regression were conducted to estimate the pooled effects of each city and effect modification by regional characteristics.

FINDINGS

Exposure to heat and cold during the entire pregnancy significantly increased the risk of PTB. The effects varied with subtypes, for medically indicated and spontaneous PTB, hazard ratios were 1·84 (95% CI: 1·29, 2·61) and 1·50 (95% CI: 1·11, 2·02) for heat, 2·18 (95% CI: 1·83, 2·60) and 2·15 (95% CI: 1·92, 2·41) for cold. The associations were stronger for PTB less than 35 weeks than those during weeks 35-36. The effects varied across locations, and GDP per capita (β=-0·16) and hospital beds per 1000 persons (β=-0·25) were protective factors for the effects.

INTERPRETATION

Extreme temperature can increase the risk of medically indicated and spontaneous PTB, and higher regional socio-economic status may moderate such effects. In the context of climate change, such findings may have important implications for protecting the health of vulnerable groups, especially newborns.

FUNDING

National Key R&D Program of China (2018YFA0606200), National Natural Science Foundation of China (42175183), Strategic Priority Research Program of the Chinese Academy of Sciences (XDA20030302), National Natural Science Foundation of China (42071377).

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.

The Association of Ambient Temperature with Extremely Preterm Births

INTRODUCTION

Extremely preterm births (EPT), require complex decision making and significant medical interventions. While environmental factors such as ambient temperature extremes have been associated with preterm births, little is known of the environmental associations with EPT births. The objective of this study is to explore whether ambient temperature is associated with increased risk of EPT birth.

METHODS

Birth records for 315,226 infants born in Queensland Australia (2007-2015) were matched to average maximum and minimum temperature for the last month of pregnancy. Odds ratios and 95% confidence intervals were calculated using a generalised linear model. Population attributable risk was calculated for a 5% reduction in maximum temperature.

RESULTS

Each one degree increase in maximum [aOR 1.03 (95% CI 1.01, 1.05)] and minimum temperature [aOR 1.02 (95% CI 1.01, 1.04)] was associated with an increase in odds for EPT birth. Increased odds for EPT births was found for maternal smoking [aOR 1.46 (95% CI 1.23, 1.72)], increasing plurality [OR 6.38 (95% CI 5.48, 7.42)] and stillbirth [aOR 342.99 (95% CI 295.53, 398.06)]. When stratified by birth status, the association was only found for live births.

DISCUSSION

Higher temperatures are associated with small increases in the odds of delivering an infant in the EPT period. The risk may be enhanced for women who smoke during pregnancy. Women at an increased risk of preterm births should be counselled around methods to reduce their exposure to excessive heat.

Preterm Delivery; Who Is at Risk?

Preterm birth (PTB) is the leading cause of perinatal morbidity and mortality. Adverse effects of preterm birth have a direct correlation with the degree of prematurity, in which infants who are born extremely preterm (24–28 weeks gestation) have the worst outcomes. We sought to determine prominent risk factors for extreme PTB and whether these factors varied between various sub-populations with known risk factors such as previous PTB and multiple gestations. A population-based retrospective cohort study was conducted. Risk factors were examined in cases of extreme PTB in the general population, as well as various sub-groups: singleton and multiple gestations, women with a previous PTB, and women with indicated or induced PTB. A total of 334,415 deliveries were included, of which 1155 (0.35%) were in the extreme PTB group. Placenta previa (OR = 5.8, 95%CI 4.14–8.34, p < 0.001), multiple gestations (OR = 7.7, 95% CI 6.58–9.04, p < 0.001), and placental abruption (OR = 20.6, 95%CI 17.00–24.96, p < 0.001) were the strongest risk factors for extreme PTB. In sub-populations (multiple gestations, women with previous PTB and indicated PTBs), risk factors included placental abruption and previa, lack of prenatal care, and recurrent pregnancy loss. Singleton extreme PTB risk factors included nulliparity, lack of prenatal care, and placental abruption. Placental abruption was the strongest risk factor for extreme preterm birth in all groups, and risk factors did not differ significantly between sub-populations.

Acute associations between heatwaves and preterm and early-term birth in 50 US metropolitan areas: a matched case-control study

BACKGROUND

The effect of heatwaves on adverse birth outcomes is not well understood and may vary by how heatwaves are defined. The study aims to examine acute associations between various heatwave definitions and preterm and early-term birth.

METHODS

Using national vital records from 50 metropolitan statistical areas (MSAs) between 1982 and 1988, singleton preterm (< 37 weeks) and early-term births (37-38 weeks) were matched (1:1) to controls who completed at least 37 weeks or 39 weeks of gestation, respectively. Matching variables were MSA, maternal race, and maternal education. Sixty heatwave definitions including binary indicators for exposure to sustained heat, number of high heat days, and measures of heat intensity (the average degrees over the threshold in the past 7 days) based on the 97.5th percentile of MSA-specific temperature metrics, or the 85th percentile of positive excessive heat factor (EHF) were created. Odds ratios (OR) for heatwave exposures in the week preceding birth (or corresponding gestational week for controls) were estimated using conditional logistic regression adjusting for maternal age, marital status, and seasonality. Effect modification by maternal education, age, race/ethnicity, child sex, and region was assessed.

RESULTS

There were 615,329 preterm and 1,005,576 early-term case-control pairs in the analyses. For most definitions, exposure to heatwaves in the week before delivery was consistently associated with increased odds of early-term birth. Exposure to more high heat days and more degrees above the threshold yielded higher magnitude ORs. For exposure to 3 or more days over the 97.5th percentile of mean temperature in the past week compared to zero days, the OR was 1.027 for early-term birth (95%CI: 1.014, 1.039). Although we generally found null associations when assessing various heatwave definitions and preterm birth, ORs for both preterm and early-term birth were greater in magnitude among Hispanic and non-Hispanic black mothers.

CONCLUSION

Although associations varied across metrics and heatwave definitions, heatwaves were more consistently associated with early-term birth than with preterm birth. This study's findings may have implications for prevention programs targeting vulnerable subgroups as climate change progresses.

Long-term digestive hospitalizations of premature infants (besides necrotizing enterocolitis): is there a critical threshold?

BACKGROUND

In this study we sought to ascertain a critical threshold of the degree of prematurity and long-term digestive morbidity of the offspring.

METHODS

A population-based cohort analysis was conducted, comparing long-term incidence of digestive morbidity in infants born preterm. Cases were divided into four groups according to the extremity of prematurity. Digestive morbidity included hospitalizations involving a predefined set of ICD9 codes. A Kaplan-Meier survival curve was constructed to compare cumulative incidence of digestive morbidity. A Cox proportional hazards model was used to control for confounders.

RESULTS

During the study period 220,563 patients met the inclusion criteria. Offspring born preterm had significantly more hospitalizations due to digestive morbidity compared to term offspring. The Kaplan-Meier survival curve demonstrated significant higher cumulative incidence of long-term digestive morbidity of the offspring with decreasing gestational age (Log rank p < 0.001). The risk was highest at 28 weeks gestation. Using a Cox proportional hazards model, being born at very and moderate to late preterm birth was independently associated with long-term digestive morbidity.

CONCLUSION

Preterm delivery is an independent risk factor for long-term digestive morbidity of the offspring. In our population, 28 weeks gestation is the critical cut-off for pronounced digestive morbidity.

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.

Association of Summer Heat Waves and the Probability of Preterm Birth in Minnesota: An Exploration of the Intersection of Race and Education

Preterm birth (PTB) is common and has negative impacts on infant health. While some maternal risk factors have been identified, including age under 20 or over 40, substance abuse, low BMI, and racism, less is known about the impact of environmental exposures like high heat. We combined 154,157 records of live births occurring in Minnesota between 2009 and 2015 with hourly weather records collected from the Minneapolis–St. Paul airport. We tested if maternal heat wave exposure (a seven-day period with a mean daily high temp of 37 °C) immediately prior to birth leads to a higher risk of preterm birth. Additional covariates included maternal age, race/ethnicity, educational status, and residence in the seven-county Minneapolis–St. Paul metro area. Pregnant women exposed to a seven-day heat wave of 37 °C or higher experienced a higher relative risk of PTB compared to women who did not experience a heat wave (1.14 risk ratio (RR), 1.0–1.3 95% confidence interval (CI)). The result is robust to controls for a woman’s age, race/ethnicity, educational attainment, place of residence, and year of the birth. Children born to Black women with college degrees who are exposed to heat waves experience a higher relative risk of PTB compared to White women with college degrees in a heat wave (2.97 RR, 1.5–6.1 95% CI). Summer heat waves are associated with higher risk of PTB in late-term pregnancies in Minnesota.

Prenatal exposure to ambient air temperature and risk of early delivery

BACKGROUND

Preterm birth is a major determinant of adverse health consequences, and early term births are also associated with increased risk of various outcomes. In light of climate change, the effect of ambient temperature on earlier delivery is an important factor to consider. Several studies have focused on associations of ambient air temperature (Ta) on preterm birth, but few have examined associations with early term births.

AIMS

To investigate the association of prenatal exposure to Ta with preterm birth (<37 completed gestation weeks) and with early-term birth (<39 completed gestation weeks) in a semi-arid climate.

METHODS

All singleton deliveries at the Soroka Medical Center from the Southern district of Israel, with estimated conception dates between May 1, 2004 and March 31, 2013 (N = 62,547) were linked to prenatal Ta estimates from a spatiotemporally resolved model, with daily 1 km resolution. We used time-dependent Cox regression models with weekly mean Ta throughout gestation, adjusted for calendar month and year of conception, ethnicity, census-level socio-economic status and population density.

RESULTS

Ta was positively associated with late preterm birth (31 + 0/7 - 36 + 6/7 weeks), with increased risk in the upper Ta quintile as compared to the third quintile, hazard ratio (HR) = 1.31, 95% confidence interval (CI) = 1.11-1.56. Ta also associated with early term birth (37 + 0/6 - 38 + 6/7), with increased risk in the upper Ta quintile as compared to the third quintile, HR = 1.24, 95% CI = 1.13-1.36.

CONCLUSION

Exposure to high ambient temperature during pregnancy is associated with a higher risk of preterm and early term birth in southern Israel.

Ambient temperature and air pollution, and the risk of preterm birth in Tehran, Iran: a time series study

Objective: The aim of the present study was to determine the relationship between temperature and air pollution, and preterm birth in Tehran, Iran.Methods: In this time series study, the daily data of preterm births, air pollution, and maximum, minimum and mean temperature from March 2015 to March 2018 were used. To evaluate the effect of air pollution and temperature with and without adjustment of their mutual effects on preterm birth in lags (days) 0-21, the Distributed Lag Non-linear Models (DLNM) was used. The relative risk (RR) was estimated for extreme, moderate and mild heat (99th, 95th, 75th percentile) and cold (1st, 5th, 25th percentile) compared with the median, and for each 10-unit increase in PM_2.5, NO₂, and O₃, 5-unit increase in SO₂, and 1-unit increase in CO.Results: The highest RR was seen in extreme (26.9 °C) and moderate (24.8 °C) heat of minimum temperature on lag 0 (RR = 1.17; 1.05-1.31, Adjusted RR = 1.16; 1.04-1.29, RR = 1.15; 1.05-1.26, Adjusted RR = 1.14; 1.03-1.25, respectively). In regard of cold, the only significant effect was for maximum temperature on lags 7-9 (RR = 1.02; 1.00-1.04). Each 10-unit increase in PM2.5 in Lag 0 (RR = 1.008; 1.001-1.014) and lag 1 (RR = 1.004; 1.001-1.007) and in NO₂ in lag 0 (RR = 1.006; 1.000-1.012) had significant effects.Conclusion: Maternal exposure to a minimum daily temperature of 26.9 and 24.8 °C compared to 13.2 °C increased the risk of preterm birth by 17 and 15% on the same day, respectively. This risk increased by 0.8 and 0.6%, on the same day for each 10-unit increase in PM_2.5 and NO₂, respectively.

Spring peaks and autumn troughs identified in peripheral inflammatory markers during the peripartum period

Seasonal variations have recently been described in biomarkers, cell types, and gene expression associated with the immune system, but so far no studies have been conducted among women in the peripartum period. It is of note that pregnancy complications and outcomes, as well as autoimmune diseases, have also been reported to exhibit seasonal fluctuations. We report here a clear-cut seasonal pattern of 23 inflammatory markers, analysed using proximity-extension assay technology, in pregnant women. The inflammatory markers generally peaked in the spring and had a trough in the autumn. During the postpartum period we found seasonality in one inflammatory marker, namely monocyte chemotactic protein 4 (MCP-4). Our findings suggest that seasonal variations in peripheral inflammatory markers are only observed during pregnancy. The results of this study could be valuable to professionals working within the field of immunology-related areas, and provide insight for the understanding of obstetric complications.

Time trends and sociodemographic determinants of preterm births in pregnancy cohorts in Matlab, Bangladesh, 1990-2014

Introduction

Preterm birth is the major cause of under-five mortality. Population-based data on determinants and proportions of children born preterm are limited, especially from low-income countries. This study aimed at assessing time trends and social, reproductive and environmental determinants of preterm births based on a population-based pregnancy cohort over 25 years in rural Bangladesh.

Methods

In this cohort study in Matlab, a rural area in Bangladesh, we used data from the Health and Demographic Surveillance System from 1990 to 2014. Gestational age at birth was based on the reported last menstrual period and verified by ultrasound assessments. Preterm birth proportions were assessed within strata of social and reproductive characteristics, and time series analysis was performed with decomposition for trend and seasonality. We also determined the prevented fractions of preterm birth reduction associated with social and demographic changes during the follow-up period.

Results

Analyses were based on 63 063 live births. Preterm birth decreased from 29% (95% CI 28.6 to 30.1) in 1990-1994 to 11% (95% CI 10.5 to 11.6) in 2010-2014. Low education, older age and multi-parity were associated with higher proportions of preterm births across the study period. Preterm births had a marked seasonal variation. A rapid increase in women's educational level and decrease in parity were associated with the decline in preterm births, and 27% of the reduction observed from 1990 to 2014 could be attributed to these educational and reproductive changes.

Conclusion

The reduction in preterm birth was to a large extent associated with the sociodemographic transition, especially changes in maternal education and parity. The persistent seasonal variation in the proportion of preterm birth may reflect the environmental stressors for pregnant women across the study period. Continued investments in girls' education and family planning programmes may contribute to further reduction of preterm births in Bangladesh.

Environmental extreme temperature and daily preterm birth in Sabzevar, Iran: a time-series analysis

Objectives

Most of the studies on the effect of heat stress on preterm birth (PTB) are conducted in temperate climates. Evidence on this effect in hot and arid countries with low and middle income is limited. This paper describes the short-term effect of exposure to the hot and cold environment on a daily number of PTB in Iran.

Methods

The daily number of PTB was obtained from all hospitals of the city. Meteorological and air pollution data from 2011 to 2017 were obtained from a metrological station in the city. A semi-parametric generalized additive model following a quasi-Poisson distribution with the distributed lag non-linear model was selected as a modeling framework for time-series analysis to simultaneously model the short-term and lagged effect of heat stress on PTB in the Sabzevar city.

Results

The minimum and maximum daily temperature were − 11.2 and 45.4 °C respectively. The highest risk estimate at extreme cold temperature was found for apparent temperature (relative risk (RR) 1.83; 95% CI 1.61: 2.09). This pattern was seen for both models. For extreme hot temperatures, the model with mean temperature showed the highest risk increase for both the main model and air pollution adjusted model (RR 1.36; 95% CI 1.25: 1.49). The lowest risk estimate in extremely cold conditions was found in the model with mean temperature. However, for extremely hot temperature conditions, the lowest risk estimate was found for both maximum and apparent temperature.

Conclusion

Obstetricians working in semi-arid areas should be aware of the influence of environmental extreme temperature on the incidence of PTB.

Electronic supplementary material

The online version of this article (10.1186/s12199-018-0760-x) contains supplementary material, which is available to authorized users.

Pregnant women may be sweeter in the summer: Seasonal changes in glucose challenge tests results. A population-based study

AIMS

A 1-hour, 50-gram glucose challenge test (GCT) is the first step in the diagnosis of gestational diabetes mellitus (GDM). Seasonal fluctuations in fasting glucose levels and GCT results were previously described. We sought to investigate seasonal changes in GCT results in a large cohort.

METHODS

GCT results were analyzed of all women insured at the Central District of Clalit Health Services (the largest health maintenance organization in Israel), between the years 2005 and 2016.

RESULTS

A total of 101,359 GCT results were analyzed. Mean GCT was 110 ± 28.9 mg/dL, and 14.5% (n = 14,652) were pathological. Both the mean and the incidence of pathological GCT were lowest in the winter, followed by spring, fall, and summer, (p for trend < 0.001). The difference in mean GCT between winter and summer was 7.82 ± 0.24 mg/dL (95% CI, 7.35-8.29). After adjustment for BMI and age, having a GCT in the winter was independently associated with the lowest risk for pathological GCT, as compared to all other seasons.

CONCLUSIONS

Seasonal changes in GCT results should be studied further in additional regions, and if found, the cutoff threshold for abnormal GCT should be re-examined and adapted to local weather conditions and seasonal variability.