Effect of heat waves and fine particulate matter on preterm births in Korea from 2010 to 2016

The modifying role of residential greenness on the association between heat waves and adverse birth outcomes: Results from the ELEFANT project

BACKGROUND

The impact of heat waves on perinatal outcomes has become a focus of attention. However, the association between heat waves and preterm birth (PTB), low birth weight (LBW), small for gestational age (SGA) and large for gestational age (LGA) remains controversial. Furthermore, whether residential greenness can mitigate the adverse effects of heat waves on birth outcomes still unclear.

METHODS

This study employed a retrospective cohort design based on data from the ELEFANT project, conducted in Tianjin, China, spanning from 2011 to 2019. We assessed heat waves exposure by creating 12 definitions of extreme heat with varying relative temperatures (90th, 95th, 97.5th and 99th percentiles) and durations (at least 2, 3, or 4 consecutive days). Residential greenness levels were evaluated using the MODIS Normalized Difference Vegetation Index (NDVI). Cox proportional hazards regression models were fitted to estimate the risks of PTB, LBW, SGA and LGA in relation to heatwaves exposure and the multiplicative and additive interactions of heat waves and greenness on adverse birth outcomes across different pregnancy periods, including pre-pregnancy.

RESULTS

Our findings indicate that heatwaves significantly increase the risks of PTB by 2.4%-15.6%, LBW by 7.6%-18 %, SGA by 3.6%-88.4%, and LGA by 2%-3.4%. The lack of residential greenness exhibited a synergistic interaction with heatwaves on PTB, SGA and LGA (RERI >0), especially during milder heat events during entire pregnancy. For LBW, interactions between greenness and heatwaves were limited. Furthermore, we identified that heatwave was significantly associated with high risk of adverse birth outcomes among mothers living in rural areas.

CONCLUSIONS

Prioritizing greenspace can help mitigate the effects of heatwaves, offering a viable and cost-effective approach to protecting maternal and fetal health.

Synergistic Toxicity of Fine Particulate Matter and Ozone and Their Underlying Mechanisms

The co-occurrence of fine particulate matter (PM2.5) and ozone has emerged as a critical environmental challenge in recent years. The individual harmful impacts of PM2.5 and ozone exposure have been well studied; however, their combined toxicity under co-exposure conditions remains mechanistically undefined. This paper provides an extensive evaluation of the current pollution levels, epidemiological investigation, and new findings on the toxicological mechanisms of combined exposure to PM2.5 and ozone. The synergistic toxicity of PM2.5 and ozone depends on different factors, including the physicochemical properties of PM2.5, the dose and duration of exposure, and the specific target organs. Through extensive research, we identified the main targets of toxic responses to PM2.5 and ozone exposure and summarized their synergistic toxic mechanisms. Given the current research priorities, there is an urgent need to improve scientific research regarding PM2.5 and ozone co-exposure with priority given to characterizing their properties and toxicological responses while updating relevant guidelines and standards.

Scoping review of climate drivers on maternal health: current evidence and clinical implications

Objective

To systematically review the literature on associations between climate drivers and health outcomes among pregnant people. This review fills a gap by synthesizing evidence for a clinician audience.

Data Sources

Systematic scoping review of articles published in PubMed and clinicaltrials.gov from January 2010 through December 2023.

Study Eligibility Criteria

Empirical studies published in English-language peer-reviewed journals, assessing associations between select climate drivers and adverse maternal and birth outcomes. The review included studies examining heat, storms, sea level rise, flooding, drought, wildfires, and other climate-related factors. Health outcomes included preterm birth, low birthweight, small for gestational age, gestational diabetes, pre-eclampsia/eclampsia, miscarriage/stillbirth and maternal mortality.

Study Appraisal and Synthesis Methods

The scoping review protocol was registered with the International Platform of Registered Systematic Review and Meta-analysis Protocols (INPLASY202410004, January 3, 2024) and conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA). Data were extracted by 2 authors; quality and risk of bias was assessed independently.

Results

Total of 966 references were screened; 16.35% (k=158) met inclusion criteria. The majority of studies (146/158; 92.4%) documented statistically significant and clinically meaningful associations between climate drivers and adverse perinatal health outcomes, including risk of preterm birth, low birthweight, and stillbirth as well as preeclampsia, gestational diabetes, miscarriage, and maternal death. Among the most durable findings: extreme heat exposure in early and late pregnancy were associated with increased risk of preterm birth and stillbirth. Driven in part by large (often population-based) studies and objective outcomes from surveillance data or medical record reviews, studies in this scoping review were evaluated as high quality (scoring 7-9 on the Newcastle-Ottawa Scale). Risk of bias was generally low.

Conclusions

Climate drivers are consistently associated with adverse health outcomes for pregnant people. Continuing education for clinicians, and clinician-patient communications should be expanded to address risks of climate change and extreme weather exposure, especially risks of extreme heat in late-pregnancy. Results from this review should inform multilevel interventions to address adverse health effects of climate during pregnancy as well as practice advisories, protocols, checklists, and clinical guidelines in obstetrics.

Extreme temperatures, PM2.5 and trajectories of impaired thyroid hormone sensitivity: A longitudinal study of patients with schizophrenia

BACKGROUND

The climate change scenario has witnessed an increase in extreme temperature events (ETEs), including heat waves and cold spells, and a heightened occurrence of compounding with fine particulate matter (PM2.5). However, the impact of this phenomenon on the sensitivity to thyroid hormones (THs) in humans is unclear, especially in a group as specific as schizophrenia.

METHODS

A longitudinal study was constructed using longitudinal measurements of thyroid function in schizophrenia in the Anhui Mental Health Center. The latent growth mixture model was applied to assess the optimal trajectory of change in impaired THs sensitivity. We then used logistic regression to explore associations between heat waves, cold spells, and PM2.5 with impaired THs sensitivity trajectories in the total population and different gender and age subgroups. Furthermore, the effect of the frequency, intensity, and duration of ETEs in the above associations was explored, as well as an assessment of the interaction between ETEs and PM2.5.

RESULTS

Among 931 participants, we identified two classifications of trajectories of impaired THs sensitivity: "Low-stable" (n = 836, 89.80 %) and "Rise-slight down" (n = 95, 10.20 %). Logistic regression showed significant associations between each additional day of heat waves (≥3 days with temperature thresholds above the 95th percentile) and cold spells (≥3 days with temperature thresholds below the 5th percentile) and "Rise-slight down" trajectory, with odds ratios (95 % confidence intervals) of 1.06 (1.02, 1.10) and 1.19 (1.14, 1.24), respectively, and the strength of this association increased with the intensity and duration of ETEs. Subgroup analyses indicated that the association was more pronounced in males and the age group above 40 years. Furthermore, PM2.5 was found to interact with heat waves, with high concentrations exacerbating the effects of heat waves.

CONCLUSIONS

Our findings suggest that mitigating both ETEs and PM2.5 exposures may bring health co-benefits in preventing thyroid impairment in schizophrenia.

Impact of Climate Change on Reproductive Health and Pregnancy Outcomes: A Systematic Review

Climate change has emerged as a significant global health challenge, with growing evidence linking environmental factors to adverse reproductive health outcomes. The primary objective of this review is to assess the effects of climate change-driven environmental factors, such as air pollution and temperature extremes, on reproductive health outcomes, including fertility rates, miscarriage, preterm birth, and congenital anomalies. A comprehensive search of PubMed, Google Scholar, and Web of Science was conducted until July 2024. Studies included in the review were observational, experimental, and randomized controlled trials that reported quantitative data on reproductive outcomes in relation to climate-related environmental exposures. A total of 49 studies were selected for qualitative synthesis. The review found that increased exposure to particulate matter (PM2.5), extreme temperatures, and proximity to traffic were consistently associated with reduced fertility, increased risks of miscarriage, preterm birth, and low birth weight. Adverse effects were particularly pronounced among vulnerable populations, such as pregnant women of lower socioeconomic status and those living in disaster-prone areas. The studies also highlighted potential transgenerational effects, with prenatal exposure to environmental stressors influencing the long-term health of offspring. The findings underscore the urgent need for public health interventions and policies to mitigate environmental exposures that negatively impact reproductive health. Future research should focus on longitudinal and interventional studies to establish causal relationships and inform effective public health strategies.

Educating Pregnant Women About the Dangers of Extreme Heat and Air Pollution

Climate change poses a serious threat to the health and well-being of pregnant women and their developing fetuses. Certain populations are at greater risk of adverse outcomes from air pollution, a contributing factor to climate change. In addition, heightened exposure to extreme heat, a consequence of climate change, exacerbates the existing health care inequities in the United States. Nurses, midwives, and other health care clinicians are uniquely positioned to reduce the harmful effects of climate change by educating pregnant women and their families and advocating for systems and policies that can decelerate climate change. The purpose of this article is to provide resources for clinicians to use in educating pregnant women about the risks of extreme heat and air pollution, their potential effects on pregnancy and neonatal outcomes, and strategies to help mitigate risk. We conclude with implications for practice, opportunities for advocacy, and areas for future research.

Heat exposure induced risks of preterm birth mediated by maternal hypertension

Heat exposure is associated with an increased risk of preterm birth (PTB), with previous work suggesting that maternal blood pressure may play a role in these associations. Here we conducted a cohort study of 197,080 singleton live births across 8 provinces in China from 2015 to 2018. The study first estimated the associations between heat exposure, maternal hypertension and clinical subtypes of PTB, and then quantified the role of maternal hypertension in heat and PTB using mediation analyses. We show that heat exposure (>85th, 90th and 95th percentiles of local temperature distributions) spanning from conception to the 20th gestational week was associated with a 15-21% increase in PTB, and a 20-22% increase in medically indicated PTB. Heat exposure is likely to increase the risk of maternal hypertension and elevated blood pressure. Maternal hypertension mediated 15.7% and 33.9% of the effects of heat exposure (>90th percentile) on PTB and medically indicated PTB, respectively. Based on this large-population study, we found that exposure to heat in early pregnancy can increase the risk of maternal hypertension, thereby affecting the incidence of PTB.

Heatwave characteristics complicate the association between PM2.5 components and schizophrenia hospitalizations in a changing climate: Leveraging of the individual residential environment

BACKGROUND

In the era characterized by global environmental and climatic changes, understanding the effects of PM2.5 components and heatwaves on schizophrenia (SCZ) is essential for implementing environmental interventions at the population level. However, research in this area remains limited, which highlights the need for further research and effort. We aim to assess the association between exposure to PM2.5 components and hospitalizations for SCZ under different heatwave characteristics.

METHODS

We conducted a 16 municipalities-wide, individual exposure-based, time-stratified, case-crossover study from January 1, 2017, to December 31, 2020, encompassing 160736 hospitalizations in Anhui Province, China. Daily concentrations of PM2.5 components were obtained from the Tracking Air Pollution in China dataset. Conditional logistic regression models were used to investigate the association between PM2.5 components and hospitalizations. Additionally, restricted cubic spline models were used to identify protective thresholds of residential environment in response to environmental and climate change.

RESULTS

Our findings indicate a positive correlation between PM2.5 and its components and hospitalizations. Significantly, a 1 μg/m3 increase in black carbon (BC) was associated with the highest risk, at 1.58% (95%CI: 0.95-2.25). Exposure to heatwaves synergistically enhanced the impact of PM2.5 components on hospitalization risks, and the interaction varied with the intensity and duration of heatwaves. Under the 99th percentile heatwave events, the impact of PM2.5 and its components on hospitalizations was most pronounced, which were PM2.5 (2-4d: 4.59%, 5.09%, and 5.09%), sulfate (2-4d: 21.73%, 23.23%, and 25.25%), nitrate (2-4d: 17.51%, 16.93%, and 20.31%), ammonium (2-4d: 27.49%, 31.03%, and 32.41%), organic matter (2-4d: 32.07%, 25.42%, and 24.48%), and BC (2-4d: 259.36%, 288.21%, and 152.52%), respectively. Encouragingly, a protective effect was observed when green and blue spaces comprised more than 17.6% of the residential environment.

DISCUSSION

PM2.5 components and heatwave exposure were positively associated with an increased risk of hospitalizations, although green and blue spaces provided a mitigating effect.

Adverse effects of temperature on perinatal and pregnancy outcomes: methodological challenges and knowledge gaps

Evidence linking temperature with adverse perinatal and pregnancy outcomes is emerging. We searched for literature published until 30 January 2023 in PubMed, Web of Science, and reference lists of articles focusing on the outcomes that were most studied like preterm birth, low birth weight, stillbirth, and hypertensive disorders of pregnancy. A review of the literature reveals important gaps in knowledge and several methodological challenges. One important gap is the lack of knowledge of how core body temperature modulates under extreme ambient temperature exposure during pregnancy. We do not know the magnitude of non-modulation of body temperature during pregnancy that is clinically significant, i.e., when the body starts triggering physiologic counterbalances. Furthermore, few studies are conducted in places where extreme temperature conditions are more frequently encountered, such as in South Asia and sub-Saharan Africa. Little is also known about specific cost-effective interventions that can be implemented in vulnerable communities to reduce adverse outcomes. As the threat of global warming looms large, effective interventions are critically necessary to mitigate its effects.

Disparities in preterm birth following the July 1995 Chicago heat wave

PURPOSE

To evaluate if changes in preterm birth (PTB, <37 weeks of gestation) incidence differed between non-Hispanic (NH) Black and NH white births following the July 1995 Chicago heat wave-among the most severe U.S. heat waves since 1950.

METHODS

We used an ecologic study design. We obtained birth data from January 1990-December 1996 from the National Vital Statistics File to calculate the mean monthly PTB incidence in Chicago's Cook County, Illinois. Births between July 1995 and February 1996 were potentially exposed to the heat wave in utero. We generated time series models for NH Black and NH white births, which incorporated synthetic controls of Cook County based on unexposed counties. We ran a secondary analysis considering socioeconomic status (SES).

RESULTS

From 1990-1996, the mean monthly PTB incidence among NH Black births was 18.6% compared to 7.8% among NH white births. The mean monthly PTB incidence among NH Black births from August 1995-January 1996 was 16.7% higher than expected (three additional PTBs per 100 live births per month [95% confidence interval (CI): 1, 5]). A similar increase occurred among low-SES NH Black births. No increase appeared among NH white births.

CONCLUSIONS

Severe heat waves may increase racial disparities in PTB incidence.

Association between early preterm birth and maternal exposure to fine particular matter (PM10): A nation-wide population-based cohort study using machine learning

Although preterm birth (PTB), a birth before 34 weeks of gestation accounts for only less than 3% of total births, it is a critical cause of various perinatal morbidity and mortality. Several studies have been conducted on the association between maternal exposure to PM and PTB, but the results were inconsistent. Moreover, no study has analyzed the risk of PM on PTB among women with cardiovascular diseases, even though those were thought to be highly susceptible to PM considering the cardiovascular effect of PM. Therefore, we aimed to evaluate the effect of PM10 on early PTB according to the period of exposure, using machine learning with data from Korea National Health Insurance Service (KNHI) claims. Furthermore, we conducted subgroup analysis to compare the risk of PM on early PTB among pregnant women with cardiovascular diseases and those without. A total of 149,643 primiparous singleton women aged 25 to 40 years who delivered babies in 2017 were included. Random forest feature importance and SHAP (Shapley additive explanations) value were used to identify the effect of PM10 on early PTB in comparison with other well-known contributing factors of PTB. AUC and accuracy of PTB prediction model using random forest were 0.9988 and 0.9984, respectively. Maternal exposure to PM10 was one of the major predictors of early PTB. PM10 concentration of 5 to 7 months before delivery, the first and early second trimester of pregnancy, ranked high in feature importance. SHAP value showed that higher PM10 concentrations before 5 to 7 months before delivery were associated with an increased risk of early PTB. The probability of early PTB was increased by 7.73%, 10.58%, or 11.11% if a variable PM10 concentration of 5, 6, or 7 months before delivery was included to the prediction model. Furthermore, women with cardiovascular diseases were more susceptible to PM10 concentration in terms of risk for early PTB than those without cardiovascular diseases. Maternal exposure to PM10 has a strong association with early PTB. In addition, in the context of PTB, pregnant women with cardiovascular diseases are a high-risk group of PM10 and the first and early second trimester is a high-risk period of PM10.

The Impact of Extreme Heat Exposure on Pregnant People and Neonates: A State of the Science Review

The relationship between heat exposure and perinatal morbidity and mortality is of increasing concern as global temperatures rise and extreme heat events become more frequent and intense. Heat exposure can lead to a multitude of harmful outcomes for pregnant individuals and neonates, including hospitalization and death. This state of the science review explored the evidence on the associations between heat exposure and negative health outcomes during pregnancy and the neonatal period. Findings suggest that improving health care provider and patient awareness of heat-related risks and implementing specific interventions could mitigate adverse outcomes. Furthermore, public health and other policy interventions are needed to increase thermal comfort and reduce societal exposure to extreme heat and related risks. Early warning systems, medical alerts, provider and patient education, and increased access to health care and thermal comfort may improve pregnancy and early life health outcomes.

Prenatal Exposure to Air Pollution and Pre-Labor Rupture of Membranes in a Prospective Cohort Study: The Role of Maternal Hemoglobin and Iron Supplementation

BACKGROUND

Exposure to air pollution in prenatal period is associated with prelabor rupture of membranes (PROM). However, the sensitive exposure time windows and the possible biological mechanisms underlying this association remain unclear.

OBJECTIVE

We aimed to identify the sensitive time windows of exposure to air pollution for PROM risk. Further, we examined whether maternal hemoglobin levels mediate the association between exposure to air pollution and PROM, as well as investigated the potential effect of iron supplementation on this association.

METHOD

From 2015 to 2021, 6,824 mother-newborn pairs were enrolled in the study from three hospitals in Hefei, China. We obtained air pollutant data [particulate matter (PM) with aerodynamic diameter ≤2.5μm (PM2.5), PM with aerodynamic diameter ≤10μm (PM10), sulfur dioxide (SO2), and carbon monoxide (CO)] from the Hefei City Ecology and Environment Bureau. Information on maternal hemoglobin levels, gestational anemia, iron supplementation, and PROM was obtained from medical records. Logistic regression models with distributed lags were used to identify the sensitive time window for the effect of prenatal exposure to air pollutant on PROM. Mediation analysis estimated the mediated effect of maternal hemoglobin in the third trimester, linking prenatal air pollution with PROM. Stratified analysis was used to investigate the potential effect of iron supplementation on PROM risk.

RESULTS

We found significant association between prenatal exposure to air pollution and increased PROM risk after adjusting for confounders, and the critical exposure windows of PM2.5, PM10, SO2 and CO were the 21th to 24th weeks of pregnancy. Every 10-μg/m3 increase in PM2.5 and PM10, 5-μg/m3 increase in SO2, and 0.1-mg/m3 increase in CO was associated with low maternal hemoglobin levels [-0.94g/L (95% confidence interval (CI): -1.15, -0.73), -1.31g/L (95% CI: -1.55, -1.07), -2.96g/L (95% CI: -3.32, -2.61), and -1.11g/L (95% CI: -1.31, -0.92), respectively] in the third trimester. The proportion of the association between air pollution and PROM risk mediated by hemoglobin levels was 20.61% [average mediation effect (95% CI): 0.02 (0.01, 0.05); average direct effect (95%): 0.08 (0.02, 0.14)]. The PROM risk associated with exposure to low-medium air pollution could be attenuated by maternal iron supplementation in women with gestational anemia.

CONCLUSIONS

Prenatal exposure to air pollution, especially in the 21st to 24th weeks of pregnancy, is associated with PROM risk, which is partly mediated by maternal hemoglobin levels. Iron supplementation in anemia pregnancies may have protective effects against PROM risk associated with exposure to low-medium air pollution. https://doi.org/10.1289/EHP11134.

Factors influencing vulnerability to climate change-related health impacts in cities - A conceptual framework

Climate change will have adverse impacts on human health, which are amplified in cities. For these impacts, there are direct, indirect, and deferred pathways. The first category is well-studied, while indirect and deferred impacts are not well-understood. Moreover, the factors moderating the impacts have received little attention, although understanding these factors is critical for adaptation. We developed a conceptual framework that shows the pathways of climate impacts on human health, focusing specifically on the factors of urban environment moderating the emergence and severity of these health impacts. Based on the framework and literature review, we illustrate the mechanisms of direct, indirect, and deferred health impact occurrence and the factors that exacerbate or alleviate the severity of these impacts, thus presenting valuable insights for anticipatory adaptation. We conclude that an integrated systemic approach to preventing health risks from climate change can provide co-benefits for adaptation and address multiple health risks. Such an approach should be mainstreamed horizontally to all sectors of urban planning and should account for the spatiotemporal aspects of policy and planning decisions and city complexity.

Interaction effects of night-time temperature and PM2.5 on preterm birth in Huai River Basin, China

Nocturnal temperature is observed increasing with global warming. However, evidence on night-time non-optimal temperature on the risk of preterm birth (PTB) is limited, and the potential interactions with air pollution on PTB has not been well clarified. We therefore conducted a population-based retrospective cohort study to evaluate the effect of night-time temperature extremes on the risk of PTB and its interaction with air pollution. Records of 196,780 singleton births from 4 counties in Huai River Basin (2013-2018) were obtained. Gridded data on night-time temperature were collected from a high-quality Chinese Air Quality Reanalysis dataset. We used a multivariate logistic regression to evaluate the effects of night-time heat and cold exposure on the risk of PTB as well as its subtypes. Potential interactions between night-time temperature extremes and fine particulate matter < 2.5 µm (PM_2.5) were examined using the relative excess risk due to interaction (RERI). We found that the risk of PTB was positively associated with third trimester night-time extremely heat and cold exposure, with adjusted OR of 1.898 (95 %CI: 1.655-2.177) and 2.044 (95 %CI: 1.786-2.339). Similar effects were observed for PTB subtypes, moderately PTB (mPTB) and very PTB (vPTB). Synergistic effects (RERI greater than 0) of each trimester night-time temperature extremes exposure and PM_2.5 on PTB were observed. We identified consistent positive interactions between night-time temperature extremes and PM_2.5 on mPTB. No significant interaction of night-time temperature extremes and PM_2.5 on vPTB was found. In conclusion, this large retrospective cohort study found that third trimester night-time heat and cold exposure significantly increased the risk of PTB and its subtypes. There is a synergistic effect between night-time temperature extremes and high PM_2.5 levels on PTB and mPTB. In the context of climate warming, our results add new evidence to the current understanding of night-time non-optimal temperature exposure on PTB.

Gestational exposure to ambient particulate matter and preterm birth: An updated systematic review and meta-analysis

Previous studies on gestational particulate matter (PM) exposure and preterm birth (PTB) showed inconsistent results, and no study systematically examined the short-term effect of PM exposure on PTB subtypes. To investigate both long- and short-term effects of the evidence to date in general population, we searched for epidemiological studies on PM exposure and PTB that published in PubMed, Web of Science, Embase and Cochrane Library up to March 31, 2022. The protocol for this review was registered with PROSPERO (CRD42021265202). Heterogeneity was assessed by Cochran's Q test and I² statistic. Publication bias was evaluated using funnel plots and Egger's tests. Subgroup analysis, meta-regression and sensitivity analysis were performed. Of 16,801 records, 84 eligible studies were finally included. The meta-analysis of long-term effect showed that per 10 μg/m³ increase in PM_2.5 and PM₁₀ during entire pregnancy were associated with PTB, the pooled odds ratios (ORs) were 1.084 (95% CI: 1.055-1.113) and 1.034 (95% CI: 1.018-1.049). Positive associations were found between PM_2.5 in second trimester and PTB subtypes. For the short-term exposure, we observed that PTB was positively associated with a 10 μg/m³ increment in PM_2.5 on lag day 2 and 3, the pooled ORs and 95% CIs were 1.003 (1.001-1.004) and 1.003 (1.001-1.005), with I² of 65.30% and 76.60%. PM₁₀ exposure on ave day 1 increased the risk of PTB, the pooled OR was 1.001 (95% CI: 1.000, 1.001). We also found that PM₁₀ exposure in 2 weeks prior to birth increased PTB risk. Our results support the hypothesis of both long- and short-term PM_2.5 exposure increase the risk of PTB. Further well-designed longitudinal studies and investigations into potential biological mechanisms are warranted.

Systematic review of climate change effects on reproductive health

Climate change is a major risk factor for overall health, including reproductive health, and well-being. Increasing temperatures, due mostly to increased greenhouse gases trapping excess heat in the atmosphere, result in erratic weather patterns, wildfires, displacement of large communities, and stagnant water resulting in vector-borne diseases that, together, have set the stage for new and devastating health threats across the globe. These conditions disproportionately affect disadvantaged and vulnerable populations, including women, pregnant persons, young children, the elderly, and the disabled. This review reports on the evidence for the adverse impacts of air pollution, wildfires, heat stress, floods, toxic chemicals, and vector-borne diseases on male and female fertility, the developing fetus, and obstetric outcomes. Reproductive health care providers are uniquely positioned and have an unprecedented opportunity to educate patients and policy makers about mitigating the impact of climate change to assure reproductive health in this and future generations.

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.