Seasonality in Birth Weight in Israel: New Evidence Suggests Several Global Patterns and Different Etiologies

Associations of COVID-19 lockdown with birth weight in China

Background

During the special period of the global spread of COVID-19, pregnant women are sensitive groups to the impacts of COVID-19 epidemic. However, the effects of lockdown measures implemented in response to the COVID-19 on fetal birthweight remain unclear.

Objectives

This study investigated the associations of COVID-19 lockdown with birth weight in Chinese population.

Methods

We collected 730,153 data of participants from hospitals of five cities in the south of China, we defined the time period of level I response (1/23-2/24/2020) as level I lockdown, and women who were pregnant during level I lockdown as the exposure group. Women who were pregnant during the same calendar month from 2015 to 2019 were defined as the unexposed group. We quantitatively estimate the individual cumulative exposure dose by giving different weights to days with different emergency response levels. Generalized linear regression models were used to estimate the association between COVID-19 lockdown exposure with birth weight and risk of low birth weight (<2,500 g) and macrosomia (>4,000 g).

Results

The birth weight of the exposed group is heavier than the unexposed group (3,238.52 vs. 3,224.11 g: adjusted β = 24.39 g [95% CI: 21.88, 26.91 g]). The exposed group had a higher risk of macrosomia (2.8% vs. 2.6%; adjusted OR = 1.17 [95% CI: 1.12, 1.22]). More obvious associations were found between COVID-19 lockdown and macrosomia in women who experienced the lockdown in their early pregnancy. Women who experienced the lockdown at their 4-7 weeks of pregnancy showed statistically significant heavier birth weight than unexposed group (after adjustment): β = 1.28 (95% CI: 1.11, 1.46) g. We also observed a positive association between cumulative exposure dose of COVID-19 lockdown in all pregnant women and birth weight, after divided into four groups, Q1: β = 32.95 (95% CI: 28.16, 37.75) g; Q2: β = 18.88 (95% CI: 14.12, 23.64) g; Q3: β = 19.50 (95% CI: 14.73, 24.28) g; Q4: β = 21.82 (95% CI: 17.08, 26.56) g. However, there was no statistically significant difference in the risk of low birth weight between exposed and unexposed groups.

Conclusions

The COVID-19 lockdown measures were associated with a heavier birth weight and a higher risk of macrosomia. Early pregnancy periods may be a more susceptible exposure window for a heavier birth weight and a higher risk of macrosomia. We also observed a positive association between cumulative exposure dose of COVID-19 lockdown and birth weight. The government and health institutions should pay attention to the long-term health of the infants born during the COVID-19 lockdown period, and follow up these mothers and infants is necessary.

Ambient temperature, heat stress and fetal growth: A review of placenta-mediated mechanisms

Pregnancy is increasingly considered a period of vulnerability for extreme heat exposure. Multiple lines of evidence support that heat stress is associated with placental insufficiency, poor fetal growth and decreased birth weight. In this narrative review, we first summarize evidence linking ambient temperature or experimentally-induced heat stress with fetal and placental growth outcomes in humans, ruminants and murine species. We then synthesize the literature on putative underlying biological pathways with a focus on the placenta. Reviewed mechanisms include: reduced uterine-placental blood flow, impaired supply of metabolic substrates to the fetus, activation of the maternal stress-response system, and disruption of other endocrine and immune system endpoints. Taken together, this body of evidence supports that exposure to extreme ambient heat likely has adverse consequences for placental development and function. However, research investigating placenta-mediated pathophysiological mechanisms in humans remains extremely limited.

Maternal exposure to extreme high-temperature, particulate air pollution and macrosomia in 14 countries of Africa

BACKGROUND

Macrosomia has increased rapidly worldwide in the past few decades, with a huge impact on health. However, the effect of PM_2.5 and extreme high-temperature (EHT) on macrosomia has been ignored.

OBJECTIVE

This study aimed to explore the association between maternal exposure to EHT, PM_2.5 and macrosomia based on the Seventh Demographic and Health Survey (DHS) in 14 countries of Africa.

METHODS

The study included detailed demographic information on 106 382 births and maternal. Satellite inversion models estimated monthly mean PM_2.5 and mean surface temperature of 2 m (SMT_2m ). Macrosomia was defined as the birth weight ≥ 4000 g. We used a Cox proportional risk regression model to estimate the association between PM_2.5 , EHT and macrosomia. We further explored the susceptibility of exposure to EHT and PM_2.5 at different pregnancy periods to macrosomia, and plotted the expose-response curve between PM_2.5 and macrosomia risk using a restricted cubic spline function. In addition, the Interplot model was used to investigate the interaction between EHT and PM_2.5 on macrosomia. Finally, some potential confounding factors were analysed by stratification.

RESULTS

There was the positive association between EHT, PM_2.5 and macrosomia, and the risk of macrosomia with the increase in concentrations of PM_2.5 without clear threshold. Meanwhile, EHT and PM_2.5 had a higher effect on macrosomia in middle/later and early/middle stages of pregnancy, respectively. There was a significant interaction between EHT and PM_2.5 on macrosomia.

CONCLUSIONS

Maternal exposure to EHT, PM_2.5 during pregnancy was associated with an increased risk of macrosomia in Africa.

Birth and prenatal care outcomes of Latina mothers in the Trump era: Analysis by nativity and country/region of origin

We examined whether and how birth outcomes and prenatal care utilization among Latina mothers changed over time across years associated with the Trump sociopolitical environment, using restricted-use birth records from the National Center for Health Statistics (NCHS). To assess potential variation among subpopulations, we disaggregated the analyses by maternal nativity and country/region of origin. Our results indicate that both US- and foreign-born Latina mothers experienced increasingly higher risks of delivering low birthweight (LBW) and preterm birth (PTB) infants over the years associated with Trump's political career. Among foreign-born Latinas, adverse birth outcomes increased significantly among mothers from Mexico and Central America but not among mothers from Puerto Rico, Cuba, and South America. Levels of inadequate prenatal care utilization remained largely unchanged among groups who saw increases in LBW and PTB, suggesting that changes in prenatal care did not generally explain the observed worsening of birth outcomes among Latina mothers during the Trump era. Results from this study draw attention to the possibility that the Trump era may have represented a source of chronic stress among the Latinx population in the US and add to the growing body of literature linking racism and xenophobia in the sociopolitical environment to declines in health among Latinx people, especially among targeted groups from Mexico and Central America.

Seasonality and Sex-Biased Fluctuation of Birth Weight in Tibetan Populations

Birth weight (BW) is a key determinant of infant mortality. Previous studies have reported seasonal fluctuation of BW. However, the responsible environmental factors remain disputable. High-altitude environment provides a great opportunity to test the current hypotheses due to its distinctive climate conditions. We collected BW data of  ~ 9000 Tibetan singletons born at Lhasa (elevation: 3660 m) from 2014 to 2018. Using regression models, we analyzed BW seasonality of highland Tibetans. Multivariate models with meteorological factors as independent variables were employed to examine responsible environmental factors accounting for seasonal variation. We compared BW, low-BW prevalence and sex ratio between highland and lowland populations, and we observed a significant seasonal pattern of BW in Tibetans, with a peak in winter and a trough in summer. Notably, there is a marked sex-biased pattern of BW seasonality (more striking in males than in females). Sunlight exposure in the 3rd trimester and barometric pressure exposure in the 2nd trimester are significantly correlated with BW, and the latter can be explained by seasonal change of oxygen partial pressure. In particular, due to the male-biased BW seasonality, we found a more serious BW reduction and higher prevalence of low-BW in males, and a skewed sex ratio in highlanders. The infant BW of highland Tibetans has a clear pattern of seasonality. The winter BW is larger than the summer BW, due to the longer sunlight exposure during the late-trimester. Male infants are more sensitive to hypoxia than female infants during the 2nd trimester, leading to more BW reduction and higher mortality.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s43657-021-00038-7.

A systematic review on the association of month and season of birth with future anthropometric measures

BACKGROUND

Prenatal factors might have some health impacts later in life. This study aims to systematically review the current literature on the association between season and month of birth with birth weight as well as with weight status in childhood.

METHODS

The search process was conducted in electronic databases, including papers published until April 2019 in ISI Web of Science, PubMed, Scopus, and Google Scholar. The following search strategy was used with MeSH terms: ("Seasons"[Mesh]) AND ("Obesity"[Mesh] OR "Pediatric Obesity"[Mesh] OR "Obesity, Abdominal"[Mesh] OR "Overweight"[Mesh] OR "Birth Weight"[Mesh] OR "Body Height"[Mesh]). After the selection process, 50 papers were included in this systematic review.

RESULTS

This review showed that individuals who are born in cold season (winter month) have higher body mass index (BMI) and weight in childhood. Birth in March was associated with lower weight and BMI in boys according to most studies. All studies, except one of them, showed that season/month of birth was not associated with birth weight.

CONCLUSIONS

This systematic review confirms a relationship between season and month of birth with birth weight and body size in childhood; however, the impact of confounding factors, for example, vitamin D status, should be considered in the underlying pathway of this association.

IMPACT

The results provide evidence for the effect of season and month of birth on body size in childhood. Our systematic review suggests that there is no pattern between birth weight and season/month of birth, and the occurrence of low birth weight was more frequent among infants who were born in summer than others. Further research should focus on identifying the impact of confounding factors, for example, vitamin D status in the underlying pathway of this association. There was response to the controversial findings about the effect of environment factors, such as season and month of birth, and future anthropometric indices, such as obesity, weight, height, and birth weight. Obesity is a complex and multifactorial disorder; the findings of the current study would be useful in determining the relationship pathway between the season and the month of birth with other underlying factors for childhood obesity.

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.

Effect of Maternal Exposure to Seasons during the Second and Third Trimesters of Pregnancy on Infant Birth Weight in Rural Bangladesh

BACKGROUND

Pregnant women belonging to agricultural communities of low- and middle-income countries often face seasonal food insecurity and energy stress.

OBJECTIVES

We aimed to investigate the effect of maternal exposure to different seasons during the second and third trimesters of pregnancy on infant birth weight in rural Bangladesh.

METHODS

Information on 3831 singleton live births was obtained from the electronic databases of Matlab Health and Demographic Surveillance System and Matlab hospital of the International Centre for Diarrhoeal Disease Research, Bangladesh. We collected information on all term births from July 2011 to June 2015 and excluded congenital anomalies and observations with missing data. Each year was divided into 3 distinct seasons: the post-aman harvest period (January-April), the height of the monsoon (May-August), and the post-aus harvest period (September-December). Seasonal exposure was measured in weeks, and multivariable linear regression models were fitted to determine the independent effect of each week of exposure of different seasons during the second and third trimesters of pregnancy on birth weight.

RESULTS

We observed peak birth weight in the post-aman harvest season, especially among infants born in March (mean ± SD: 2930.5 ± 462.1 g), and the lowest birth weight in the month of July (2830.6 ± 385.4 g) during the monsoon season. Regression analysis showed that exposure to the post-aman harvest season during the third trimester, and the post-aus harvest period during the second trimester of pregnancy had significant positive effects on birth weight. In the final adjusted model, each week of exposure to the post-aman harvest season during the third trimester was associated with a 6.3-g (95% CI: 1.6, 10.9 g; P = 0.008) increase in birth weight.

CONCLUSIONS

Infants born to women who were exposed to the post-aman harvest season for the entire third trimester (14 wk) were associated with 88.2-g higher weight at birth. Further investigations into the complex interplay between seasonal energy stress, maternal, and fetal nutrition and measures to alleviate it are warranted.

Adverse neonatal outcomes in relation to ambient temperatures at birth: A nationwide survey in Taiwan

This study investigated the temperature-specific risks of adverse neonatal outcomes in Taiwan. Over 2 million births between 2001 and 2010 were correlated with the daily mean outdoor temperatures at birth. A log-binomial model was used to estimate the risk of adverse neonatal outcomes in relation to ambient temperature at birth after adjusting for possible confounders. There was a significant correlation of temperature extremes with stillbirth, preterm birth, and low birth weight. Maternal exposure to temperature extremes carried greater risks of stillbirth (> 23.4°C), preterm birth (< 19.5°C and > 25.4°C), and low birth weight (< 15.5°C and > 23.4°C) than did temperatures of 21.5°C∼23.4°C. In conclusion, infants born to women exposed to temperature extremes possess greater risks for stillbirth, preterm birth, and low birth weight. The data suggest optimal temperatures to minimize overall adverse neonatal outcomes are 21.5°C∼23.4°C.

Temperature during pregnancy influences the fetal growth and birth size

BACKGROUND

Birth weight and length have seasonal fluctuations. However, it is uncertain which meteorological element has an effect on birth outcomes and which timing of pregnancy would explain such effect. Therefore, the purpose of this study was to examine temperature effects during pregnancy and which timing of pregnancy has effects on size at birth.

METHODS

A large, randomized, controlled trial of food and micronutrient supplementation for pregnant women was conducted in Matlab, Bangladesh (MINIMat Study), where women were enrolled from November 2001 to October 2003. The fetal growth data which included the size at birth and information of their mothers were obtained (n = 3267). Meteorological data such as temperature, precipitation, relative humidity, and daily sunshine hours during pregnancy were observed at the nearest observatory site of Bangladesh Meteorological Department.

RESULTS

Infants born in colder months (November-January) were shorter than those born in hot and dry, and monsoon months (mean (SD) of birth length was 47.5 cm (2.2) vs. 47.8 cm (2.1) vs. 47.9 cm (2.1) respectively; P < 0.001). Increased temperature during the last month of pregnancy was significantly related with increased birth length with adjustment for gestational weeks and the season at birth, and remained significant with further adjustments for precipitation, sex of infants, maternal early-pregnancy BMI, parity, and education status of the mother (P < 0.01). On the other hand, increased temperature at mid-gestation was associated with increased birth weight (P < 0.05).

CONCLUSIONS

These findings suggest that temperature affects both birth weight and length. The more temperature increased at the last month of pregnancy, birth length became longer. For birth weight, the temperature at mid-pregnancy affected in a positive way.

No seasonality of birth in BMI at 7years of age

Seasonal variation in birth weight was found in a previous Danish study. In the present study we investigated if the seasonality in birth weight tracked into BMI at 7years of age, but found no seasonality of birth in either BMI, overweight, or obesity.

Relationship of ambient air pollutants and hazardous household factors with birth weight among Bedouin-Arabs

BACKGROUND

Air pollution and meteorology exposures during pregnancy have been suggested to be associated with Birth Weight (BW). Yet, the individual medical background and close household environment is rarely addressed. We aimed to evaluate the independent association of BW with meteorological and air pollution exposures during pregnancy, in addition to individual, parental and household risk factors, among the Bedouin-Arab population in Southern Israel; a semi nomadic population, featured by low socio-economic levels and poor housing and household environment.

METHODS

In a retrospective cohort study we enrolled pregnant women upon their arrival in the local hospital for delivery during December 2011-April 2013. We interviewed the women and collected data on socio-demographic characteristics, medical history and household environmental hazards. Air pollution (NO2, SO2, CO, Ozone and Particulate Matter <2.5 μ and 10 μ in diameter) and meteorological data (temperature, relative humidity), retrieved from 13 monitoring sites, were linked to each woman based on the proximity of her residential address.

RESULTS

A total of 959 women were eligible for the study, half of them resided in temporary tribal localities. Ozone IQR elevation in the 3rd trimester was associated with 0.119 gr decrease in BW (95%CI -0.127 gr; -0.112 gr); temperature IQR elevation in the 3rd trimester was associated with 0.002 gr (95%CI -0.004 gr; -0.001 gr) decrease in BW. Waste in the house surroundings was associated with a decrease of 117.27 gr in BW (95%CI -209.19 gr; -25.34 gr).

CONCLUSION

Although exposure to high levels of temperature and O3 were associated with lower BW, the contribution of poor household environment indicators to BW reduction was substantially higher.

Season of birth is associated with birth weight, pubertal timing, adult body size and educational attainment: a UK Biobank study

Season of birth, a marker of in utero vitamin D exposure, has been associated with a wide range of health outcomes. Using a dataset of ∼450,000 participants from the UK Biobank study, we aimed to assess the impact of this seasonality on birth weight, age at menarche, adult height and body mass index (BMI). Birth weight, age at menarche and height, but not BMI, were highly significantly associated with season of birth. Individuals born in summer (June-July-August) had higher mean birth weight (P = 8 × 10^-10), later pubertal development (P = 1.1 × 10^-45) and taller adult height (P = 6.5 × 10^-9) compared to those born in all other seasons. Concordantly, those born in winter (December-January-February) showed directionally opposite differences in these outcomes. A secondary comparison of the extreme differences between months revealed higher odds ratios [95% confidence intervals (CI)] for low birth weight in February vs. September (1.23 [1.15-1.32], P = 4.4 × 10^-10), for early puberty in September vs. July (1.22 [1.16-1.28], P = 7.3 × 10^-15) and for short stature in December vs. June (1.09 [1.03-1.17], P = 0.006). The above associations were also seen with total hours of sunshine during the second trimester, but not during the first three months after birth. Additional associations were observed with educational attainment; individuals born in autumn vs. summer were more likely to continue in education post age 16 years (P = 1.1 × 10^-91) or attain a degree-level qualification (P = 4 × 10^-7). However, unlike other outcomes, an abrupt difference was seen between those born in August vs. September, which flank the start of the school year. Our findings provide support for the 'fetal programming' hypothesis, refining and extending the impact that season of birth has on childhood growth and development. Whilst other mechanisms may contribute to these associations, these findings are consistent with a possible role of in utero vitamin D exposure.

Secular trends in seasonal variation in birth weight

BACKGROUND

Many environmental factors have been shown to influence birth weight (BW) and one of these are season of birth.

AIM

The aim of the present study was to investigate the seasonal variation in BW in Denmark during 1936-1989, and to see if the variation could be explained by sunshine exposure during pregnancy.

METHODS

The study population was selected from the Copenhagen School Health Records Register and included 276 339 children born between 1936 and 1989. Seasonal variation was modeled using a non-stationary sinusoidal model that allowed the underlying trend in BW and the amplitude and phase of the yearly cycles to change.

RESULTS

There was a clear seasonal pattern in BW which, however, changed gradually across the study period. The highest BWs were seen during fall (September - October) from 1936 to 1963, but a new peak gradually grew from the early 1940s during early summer (May - June) and became the highest from 1964 to 1989. The amplitude of the fall peak started at 25.5 (95%CI 24.6; 25.9) grams and gradually disappeared. The amplitude of the early summer peak gradually arose from nothing to a peak of 18.6 (95%CI 17.7; 19.6) grams in the mid 1980s where it started to decrease again. Sunshine did not explain the seasonal variation in BW.

CONCLUSION

There was a clear seasonal pattern in BW in Denmark 1936-1989, which however changed across the study period. Throughout the study period we observed a peak in BW during the fall, but gradually, starting in the early 1940s, an additional early summer peak emerged and became the highest from 1964 and onwards.

Exposure to seasonal temperatures during the last month of gestation and the risk of preterm birth in Stockholm

Recent evidence from studies performed mainly in warm climates suggests an association between exposure to extreme temperatures late in pregnancy and an increased risk of preterm delivery. However, there have been fewer studies on the effect of low temperatures. The aim of this study is to explore the potential association between both heat and cold during late pregnancy and an increased risk of preterm birth in the northern location of Stockholm, Sweden. All singleton spontaneous births that took place in greater Stockholm (1998–2006) were included. Non-linear and delayed effects of mean temperature on the risk of preterm birth were explored through distributed lag non-linear models. Extreme and moderate heat and cold were estimated separately through quasi-Poisson regression analysis in two seasonal periods (heat in warm season, cold in cold season). The risk of preterm birth increased by 4%–5% when the mean temperature reached the 75th percentile (moderate heat) four weeks earlier (reference: the annual median value), with a maximum cumulative risk ratio of 2.50 (95% confidence interval: 1.02–6.15). Inconsistent associations were obtained for cold and extreme heat. Exposure to moderately high temperatures during late pregnancy might be associated with an increase in risk of preterm birth in Stockholm.

Seasonality modifies the effect of a lipid-based nutrient supplement for pregnant rural women on birth length

BACKGROUND

Maternal nutritional status is a major determinant of low birth weight and fluctuates across seasons. Seasonality may influence the outcome of prenatal nutrition interventions that aim to enhance fetal growth.

OBJECTIVE

This study investigated seasonal modifications of the efficacy of a randomized controlled prenatal nutrition intervention trial in pregnant women to improve fetal growth in rural Burkina Faso.

METHODS

The second Micronutriments et Santé de la Mère et de l'Enfant study compared a lipid-based nutrient supplement (LNS) fortified with multiple micronutrients (MMNs) to an MMN supplement. Truncated Fourier series were used to characterize seasonality in birth outcomes. Models that included the Fourier series and newborn and maternal characteristics were used to assess seasonal effect modifications of prenatal supplementation on birth outcomes.

RESULTS

Birth weight, birth length, small for gestational age as a proxy for intrauterine growth retardation, and preterm birth were significantly related to date of birth and showed important seasonal variations. LNSs, which supply energy in addition to MMNs, resulted in a significant increase in birth length (+13.5 mm, 95% CI: 6.5, 20.5 mm) at the transition from rain to dry season (September to November) compared to MMNs alone.

CONCLUSIONS

The climatologic and agricultural seasonal patterns in Burkina Faso affect the efficacy of prenatal LNSs on birth length. In this context, prenatal MMN supplementation programs should be complemented by energy supplementation during the annual rain season to promote fetal growth. This trial was registered at clinicaltrials.gov as NCT00909974.

Extreme winter temperature and birth defects: a population-based case-control study

BACKGROUND/OBJECTIVE

We examined the relationship between extreme winter temperatures and birth defects to determine whether pregnant women might be vulnerable to the weather extremes expected with climate change.

METHODS

In this population-based, case-control study, we linked the New York State Congenital Malformations Registry to birth certificates (1992-2006). Cases were defined as live births with birth defects, and controls were selected from a 10% random sample of live births. We assigned meteorological data based on maternal birth residence and summarized universal apparent temperature across gestational weeks 3-8 (embryogenesis). We defined an extreme cold day as a day with mean temperature below the 10th percentile of the regional winter temperature distribution and a cold spell as 3 consecutive extreme cold days. We averaged temperature for each week of the first trimester to identify susceptible periods. We estimated adjusted odds ratios (ORs) and 95% confidence intervals (CIs) with multivariable logistic regression for 30 birth defects groups.

RESULTS

Among 13,044 cases and 59,884 controls with at least 1 week of embryogenesis in winter, coarctation of the aorta was associated with a 1°C decrease in mean universal apparent temperature (OR 1.06, 95% CI 1.02-1.11), cold spell (OR 1.61, 95% CI 1.11-2.34), and number of extreme cold days. We observed reduced odds of hypoplastic left heart syndrome and dislocated hip for some cold indicators.

CONCLUSIONS

Most birth defects were not associated with cold indicators; however, we found positive associations between cold indicators and coarctation of the aorta in the biologically-relevant developmental window which warrants replication.

Associations of meteorology with adverse pregnancy outcomes: a systematic review of preeclampsia, preterm birth and birth weight

The relationships between meteorology and pregnancy outcomes are not well known. This article reviews available evidence on the relationships between seasonality or meteorology and three major pregnancy outcomes: the hypertensive disorders of pregnancy (including preeclampsia, eclampsia and gestational hypertension), gestational length and birth weight. In total 35, 28 and 27 studies were identified for each of these outcomes. The risks of preeclampsia appear higher for women with conception during the warmest months, and delivery in the coldest months of the year. Delivery in the coldest months is also associated with a higher eclampsia risk. Patterns of decreased gestational lengths have been observed for births in winter, as well as summer months. Most analytical studies also report decreases in gestational lengths associated with heat. Birth weights are lower for deliveries occurring in winter and in summer months. Only a limited number of studies have investigated the effects of barometric pressure on gestational length or the effects of temperature and sunshine exposure on birth weight, but these questions appear worth investigating further. Available results should encourage further etiological research aiming at enhancing our understanding of the relationships between meteorology and adverse pregnancy outcomes, ideally via harmonized multicentric studies.

Catching up from early nutritional deficits? Evidence from rural Ethiopia

We examine the nutritional status of a cohort of poor Ethiopian children and their patterns of catch-up growth in height-for-age between three key development stages: age one, five and eight. We use ordinary least squares (within community) and instrumental variables analysis. During the earliest period, we find that nutritional catch-up patterns vary substantially across socioeconomic groups: average catch-up growth in height-for-age is almost perfect among children in relatively better-off households, while among the poorer children, relative height is more persistent. Between five and eight years of age, however, we find near-perfect persistence and no evidence of heterogeneity in catch-up growth. Our findings suggest that household wealth, and in particular access to services, can lead to substantial catch-up growth early on in life. However, for our sample, the window of opportunity to catch up appears to close as early as the age of five.

The association of season and temperature with adverse pregnancy outcome in two German states, a time-series analysis

Background

A seasonality of low birth weight (LBW) and preterm birth (PTB) has been described for most regions and there is evidence that this pattern is caused by ambient outdoor temperature. However, the association as such, the direction of effect and the critical time of exposure remain controversial.

Methods

Logistic, time-series regression was performed on nearly 300,000 births from two German states to study the association between season and daily mean temperature and changes in daily proportions of term LBW (tLBW) or PTB. Analyses were adjusted for time-varying factors. Temperature exposures were examined during different periods of pregnancy.

Results

Weak evidence for an association between season of conception, season of birth or ambient outdoor temperature and tLBW or PTB was found. Results of analyses of temperature were not consistent between the two states. Different sources of bias which would have artificially led to stronger findings were detected and are described.

Conclusions

No clear evidence for an association between season of conception, season of birth or temperature and tLBW or PTB was found. In the study of pregnancy outcome different sources of bias can be identified which can potentially explain heterogeneous findings of the past.

The influence of season and ambient temperature on birth outcomes: a review of the epidemiological literature

Seasonal patterns of birth outcomes, such as low birth weight, preterm birth and stillbirth, have been found around the world. As a result, there has been an increasing interest in evaluating short-term exposure to ambient temperature as a determinant of adverse birth outcomes. This paper reviews the epidemiological evidence on seasonality of birth outcomes and the impact of prenatal exposure to ambient temperature on birth outcomes. We identified 20 studies that investigated seasonality of birth outcomes, and reported statistically significant seasonal patterns. Most of the studies found peaks of preterm birth, stillbirth and low birth weight in winter, summer or both, which indicates the extremes of temperature may be an important determinant of poor birth outcomes. We identified 13 studies that investigated the influence of exposure to ambient temperature on birth weight and preterm birth (none examined stillbirth). The evidence for an adverse effect of high temperatures was stronger for birth weight than for preterm birth. More research is needed to clarify whether high temperatures have a causal effect on fetal health.

Psoriasis and pregnancy outcomes: a nationwide population-based study

BACKGROUND

Previous research regarding pregnancy outcomes in women with psoriasis either used selective hospital-based data, or analyzed obstetric, but not infant-specific, outcomes.

OBJECTIVE

We sought to investigate whether maternal psoriasis was associated with increased risk of adverse pregnancy outcomes, compared with unaffected mothers, in an unselected nationwide population-based data set.

METHODS

In total, 1463 mothers with psoriasis and 11,704 randomly selected mothers without psoriasis were included. Of the 1463 mothers with psoriasis, 645 (44.1%) who had received photochemotherapy or systemic therapy within 2 years before their index deliveries were put in the severe psoriasis group. Conditional logistic regression analyses were conducted to calculate the risk of low birth weight (LBW), preterm birth, cesarean section, small for gestational age, and preeclampsia or eclampsia for these two groups, after adjusting for characteristics of the mother, father, and infant.

RESULTS

The odds of LBW for women with severe psoriasis were 1.40 times those of mothers without psoriasis (95% confidence interval = 1.04-1.89) after adjusting for characteristics of the mother, father, and infant. However, mothers with mild psoriasis had no significantly higher odds of LBW, preterm birth, cesarean section, infants small for gestational age, and preeclampsia or eclampsia compared with those without psoriasis.

LIMITATIONS

Patients with psoriasis were identified by diagnostic code in database, resulting in the possibility of misclassification bias. In addition, lack of information regarding maternal risk behaviors and previous adverse pregnancy outcomes may leave residual confounding.

CONCLUSION

We found that pregnant women with severe psoriasis had an increased risk of LBW infants, whereas mild psoriasis was not associated with excess risk of adverse birth outcomes.

Season of birth and subsequent body size: the potential role of prenatal vitamin D

OBJECTIVES

The relationship between season of birth and various physical and psychological outcomes was reported in many studies, although the underlying mechanism still remains unrecognized. The aim of this study was to explore the season-of-birth effect on body size in the sample of 1,148 eight-year-old Polish urban children and propose the mechanism responsible for this effect.

METHODS

The children were examined three times at their birthdays and at two cross-sectional surveys. Effects of the season of birth were checked by fitting the cosine function to empirical values and by comparison between two groups born in different periods of the year.

RESULTS

Data gathered at three examinations led to the same results: season-of-birth effect occurred only in boys and only in those relatively shortly breastfed and/or descended from the families of low-socioeconomic status. Specifically, the individuals born in October-April were taller (by 2-3 cm), heavier (by 2-3 kg), and fatter than those born in May-September.

CONCLUSIONS

The following explanatory mechanism has been formulated: insolation in Poland is minimal in November-February (winter period), and so ultraviolet absorption and vitamin D production is then the lowest. Vitamin D regulates embryo's cellular differentiation, and its deficiency triggers permanent developmental changes. Therefore, individuals conceived in autumn (i) are at the greatest risk of early vitamin D deficiency, (ii) are born in summer, and (iii) are relatively small in their further lives. The contribution of low-socioeconomic status, short breastfeeding, and being a male to the occurrence of the season-of-birth effect is also discussed.

Sinusoidal cox regression-a rare cancer example

Evidence of an association between survival time and date of birth would suggest an etiologic role for a seasonally variable environmental exposure occurring within a narrow perinatal time period. Risk factors that may exhibit seasonal epidemicity include diet, infectious agents, allergens, and antihistamine use. Typically data has been analyzed by simply categorizing births into months or seasons of the year and performing multiple pairwise comparisons. This paper presents a statistically robust alternative, based upon a trigonometric Cox regression model, to analyze the cyclic nature of birth dates related to patient survival. Disease birth-date results are presented using a sinusoidal plot with peak date(s) of relative risk and a single P value that indicates whether an overall statistically significant seasonal association is present. Advantages of this derivative-free method include ease of use, increased power to detect statistically significant associations, and the ability to avoid arbitrary, subjective demarcation of seasons.

Association of birth weight and length with air temperature, sunlight, humidity and rainfall in the city of Warsaw, Poland

Several studies have shown the month of birth effect on birth weight and height of children. The mechanism of this phenomenon is not fully explained. Using data from Warsaw hospitals, the influence of four climatic factors (temperature, sunlight, humidity and rainfall) on birth outcomes was studied. The sample consisted of 10,631 neonates (5450 boys and 5181 girls) born between May 2004 and April 2005. Individual values for birth weight and length were standardised on the overall mean and standard deviation for all subjects, separately for each sex. Differences in means of Z-score birth outcomes between months, seasons and semi-annual periods of birth were assessed by one-way analysis of variance, separately for each sex. The relation between average values of four atmospheric factors and average neonatal outcomes for each month of birth was assessed by a weighted Spearman rank correlation. The results revealed significant differences in average Z-scores of neonate weight and length between months of birth for boys and girls. Significant seasonal variation in Z-scores means was only found for birth length in boys. The correlation between four atmospheric factors during pregnancy and birth length was the highest for boys and occurred in the second trimester. Second trimester of fetal growth is the period most sensitive to influences of climatic factors.

Season of birth and risk for adult onset glioma

Adult onset glioma is a rare cancer which occurs more frequently in Caucasians than African Americans, and in men than women. The etiology of this disease is largely unknown. Exposure to ionizing radiation is the only well established environmental risk factor, and this factor explains only a small percentage of cases. Several recent studies have reported an association between season of birth and glioma risk. This paper reviews the plausibility of evidence focusing on the seasonal interrelation of farming, allergies, viruses, vitamin D, diet, birth weight, and handedness. To date, a convincing explanation for the occurrence of adult gliomas decades after a seasonal exposure at birth remains elusive.

Methodological issues in studies of air pollution and reproductive health

In the past decade there have been an increasing number of scientific studies describing possible effects of air pollution on perinatal health. These papers have mostly focused on commonly monitored air pollutants, primarily ozone (O(3)), particulate matter (PM), sulfur dioxide (SO(2)), carbon monoxide (CO), and nitrogen dioxide (NO(2)), and various indices of perinatal health, including fetal growth, pregnancy duration, and infant mortality. While most published studies have found some marker of air pollution related to some types of perinatal outcomes, variability exists in the nature of the pollutants and outcomes associated. Synthesis of the findings has been difficult for various reasons, including differences in study design and analysis. A workshop was held in September 2007 to discuss methodological differences in the published studies as a basis for understanding differences in study findings and to identify priorities for future research, including novel approaches for existing data. Four broad topic areas were considered: confounding and effect modification, spatial and temporal exposure variations, vulnerable windows of exposure, and multiple pollutants. Here we present a synopsis of the methodological issues and challenges in each area and make recommendations for future study. Two key recommendations include: (1) parallel analyses of existing data sets using a standardized methodological approach to disentangle true differences in associations from methodological differences among studies; and (2) identification of animal studies to inform important mechanistic research gaps. This work is of critical public health importance because of widespread exposure and because perinatal outcomes are important markers of future child and adult health.

Season of birth, daylight hours at birth, and high myopia

PURPOSE

Mandel et al recently reported that season of birth and daylight hours (photoperiod) at birth were associated with moderate and high levels of myopia in Israeli conscripts. We sought to investigate whether these associations were evident in subjects from the United Kingdom (UK).

DESIGN

Retrospective cross-sectional study.

PARTICIPANTS

The study population comprised 74,459 subjects aged 18 to 100 years attending UK optometry practices for an eye examination.

METHODS

Data comprising non-cycloplegic spectacle prescription, sex, date of birth, and date of eye examination were collected from UK optometry practices. The average refractive error in fellow eyes was used to classify the degree of myopia in diopters (D) for each subject as follows: absent (>-0.75 D), low (-0.75 to -2.99 D), moderate (-3.00 to -5.99 D), or high (<-6.00 D). The average monthly hours of daylight for London, UK, were classified into 1 of 4 "photoperiod categories," following Mandel et al. The odds ratio (OR) for each level of severity of myopia was calculated using multivariate logistic regression with age, sex, and either season of birth or photoperiod category as risk factors.

MAIN OUTCOME MEASURES

The OR for season of birth and photoperiod category as potential risk factors for myopia.

RESULTS

Season of birth was significantly associated with the presence of high myopia: Subjects born in summer or autumn were more likely to be highly myopic compared with those born in winter (summer OR=1.17; 95% confidence interval [CI], 1.05-1.30; P=0.006; autumn OR=1.16; 95% CI, 1.04-1.30; P=0.007). However, season of birth was not a significant risk factor for low or moderate myopia. Photoperiod category was weakly associated with low myopia (OR=0.94; 95% CI, 0.89-0.99; P=0.019), but with a direction of effect opposite to that observed by Mandel et al.

CONCLUSIONS

As in Israel, a disproportionate number of UK high myopes were born in summer or autumn rather than in winter. However, unlike the situation in Israel, this association does not seem to be related to daylight hours during the postnatal period, implicating alternative physiologic influences that vary with season, such as birth weight.

A method to model season of birth as a surrogate environmental risk factor for disease

Environmental exposures, including some that vary seasonally, may play a role in the development of many types of childhood diseases such as cancer. Those observed in children are unique in that the relevant period of exposure is inherently limited or perhaps even specific to a very short window during prenatal development or early infancy. As such, researchers have investigated whether specific childhood cancers are associated with season of birth. Typically a basic method for analysis has been used, for example categorization of births into one of four seasons, followed by simple comparisons between categories such as via logistic regression, to obtain odds ratios (ORs), confidence intervals (CIs) and p-values. In this paper we present an alternative method, based upon an iterative trigonometric logistic regression model used to analyze the cyclic nature of birth dates related to disease occurrence. Disease birth-date results are presented using a sinusoidal graph with a peak date of relative risk and a single p-value that tests whether an overall seasonal association is present. An OR and CI comparing children born in the 3-month period around the peak to the symmetrically opposite 3-month period also can be obtained. Advantages of this derivative-free method include ease of use, increased statistical power to detect associations, and the ability to avoid potentially arbitrary, subjective demarcation of seasons.

Body height differentiation by season of birth: Girls from Cracow, Poland

Published studies world wide demonstrate that measures of human development and health status vary depending on the month of birth but these patterns are not always consistent and sometimes even conflict. Direct factors related to the birth season that may significantly differentiate morphological and functional traits and mechanisms causing these relations have not been found so far. On the basis of cross-sectional material, gathered in the years 1983 and 2000 by the Department of Anthropology of the Academy of Physical Education in Cracow, two main hypotheses have been verified: (1) average body height differences by month of birth are statistically insignificant, (2) the magnitude of these differences does not change with time. Metric data of 4672 girls aged 5-18 years, born in 1965-1978 and 1982-1995, were used. The total sample was also subdivided into prepubertal (5-9 years) and adolescent (10-18 years) groups. The age of the individuals was calculated to the nearest day and the procedure of standardization on the interpolated values of regional norms was applied. A highly significant relationship between the birth month and average values of height was revealed in preadolescent girls. The results obtained for the entire material proved insignificant. The patterns of the month-of-birth effect on body height for girls born in 60./70. and 80./90. show high similarity, though the effect seems weaker in the latter sample. Winter proved to be the most favorable birth season for later body height.