IMPORTANCE Knowledge of whether serious adverse pregnancy outcomes are associated with increasingly widespread effects of climate change in the US would be crucial for the obstetrical medical community and for women and families across the country.OBJECTIVE To investigate prenatal exposure to fine particulate matter (PM 2.5 ), ozone, and heat, and the association of these factors with preterm birth, low birth weight, and stillbirth. EVIDENCE REVIEWThis systematic review involved a comprehensive search for primary literature in Cochrane Library, Cochrane Collaboration Registry of Controlled Trials, PubMed, ClinicalTrials.gov website, and MEDLINE. Qualifying primary research studies included human participants in US populations that were published in English between January 1, 2007, and April 30, 2019. Included articles analyzed the associations between air pollutants or heat and obstetrical outcomes. Comparative observational cohort studies and cross-sectional studies with comparators were included, without minimum sample size. Additional articles found through reference review were also considered. Articles analyzing other obstetrical outcomes, non-US populations, and reviews were excluded. Two reviewers independently determined study eligibility. The Arskey and O'Malley scoping review framework was used. Data extraction was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guideline. FINDINGS Of the 1851 articles identified, 68 met the inclusion criteria. Overall, 32 798 152 births were analyzed, with a mean (SD) of 565 485 (783 278) births per study. A total of 57 studies (48 of 58[84%] on air pollutants; 9 of 10 [90%] on heat) showed a significant association of air pollutant and heat exposure with birth outcomes. Positive associations were found across all US geographic regions. Exposure to PM 2.5 or ozone was associated with increased risk of preterm birth in 19 of 24 studies (79%) and low birth weight in 25 of 29 studies (86%). The subpopulations at highest risk were persons with asthma and minority groups, especially black mothers. Accurate comparisons of risk were limited by differences in study design, exposure measurement, population demographics, and seasonality. CONCLUSIONS AND RELEVANCEThis review suggests that increasingly common environmental exposures exacerbated by climate change are significantly associated with serious adverse pregnancy outcomes across the US.

INTRODUCTION: Toxic environmental exposures, specifically climate-change related exposures, pose a unique risk to pregnant women and the developing fetus. Robust evidence analysis is needed to guide clinicians on risk assessment and clinical counseling. METHODS: A literature search was conducted by our research team and medical librarian; scope included United States studies from 2007 to 2017. Climate-change related exposures included air pollution components: fine particulate matter (PM 2.5) and ozone, extreme weather, heat and temperature. Exposures ranged throughout all trimesters. Obstetrics outcomes included preterm birth, low birth-weight, and stillbirth. Exposures related to natural disasters were excluded; clinical outcomes related to neurodevelopment, mental illness, gynecology, and fertility were excluded. The Arksey and O'Malley scoping review framework was followed and quality assessment was performed using the Jadad scale. RESULTS: A total of 1,842 references were screened. 24 studies related to air pollution and preterm birth met inclusion; 21 found an effect. 27 studies related to air pollution and low birth-weight and met inclusion; 25 found an effect. 4 studies related to air pollution and stillbirth met inclusion; 3 found an effect. 5 studies related to heat and preterm birth met inclusion; 5 found an effect. 3 studies related to heat and low birth-weight met inclusion; 3 found an effect. 2 studies related to heat and stillbirth met inclusion; 2 found an effect. CONCLUSION: Climate-change related exposures, specifically air pollution and heat, are associated with an effect on important obstetrics outcomes: preterm birth, low birthweight, and stillbirth. Women's health providers should become familiar with this emerging risk.

Mission:The Permanente Journal is published for physicians and nurses to create and deliver superior health care through the principles and benefits of Permanente Medicine.Permanente Medicine is preventive, innovative, evidence-based, population care practiced by a multispecialty group, using an electronic health and medical record, and focused on patient relationships and outcomes.