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A recent systematic review found that climate change-related exacerbation of the two exposures may be having an adverse effect on obstetric outcomes.
The effects of climate change, such as increased air pollution and heat exposure, continue to encroach on and negatively impact human health. A recent systematic review found that climate change-related exacerbation of the two exposures may be having an adverse effect on obstetric outcomes1.
The systematic review, published in JAMA Network Open, evaluated existing evidence on the association between air pollution and heat on preterm birth (PTB), low birth weight (LBW), and stillbirth across the United States.
Specifically they studied prenatal exposure to fine particulate matter, ozone, and heat. Two components of air pollution that are exacerbated by continued fossil fuel use and the larger climate crisis are fine particle matter less than 2.5 µm in diameter (PM2.5) and ozone.
The associations between adverse birth outcomes and PM2.5, ozone, and heat have been studied on a global scale, but this review concentrated specifically on outcomes in the U.S. population.
The authors performed comprehensive literature searches using the ClinicalTrials.gov website, PubMed, MEDLINE, Cochrane Library, and Cochrane Collaboration Registry of Controlled Trials, and identified only studies published from January 1, 2007 to April 30, 2019.
Sixty-eight articles were examined, representing 32 million births. Twenty-nine studies analyzed risk of PTB; 32 studies analyzed LBW; and 7 analyzed stillbirths. Of these, 48 studies (84%) found a significant association between exposure to air pollutants and adverse birth outcomes.
Nine of the 10 articles that examined heat exposure and obstetrical outcomes found a significant association between exposure to heat during pregnancy and adverse birth outcomes. Although there are limitations of including a diverse group of studies, as described in the accompanying commentary by Giudice2, the findings are strengthened due to the heterogeneity.
The review included 24 studies evaluating the association of maternal exposure to PM2.5 and/or ozone with PTB, and 79% (19) of them found an increased risk. The remaining five studies showed no association, measuring exposures during the whole pregnancy, by trimester, or by month of birth.
Studies of prenatal ozone exposure either during the whole pregnancy, the third trimester, or the week before delivery found a range of increased risk of stillbirth from 3% to 39%.
Five studies on the association of maternal exposure to heat with PTB were considered, with 4 (80%) finding increased risk. The risk of preterm birth increased 11.6% per 5.6oC increase. Of the 3 studies evaluating maternal exposure and LBW, all found increased risk.
The authors also found that women with medical conditions, such as asthma, may be particularly susceptible to adverse outcomes, such as PTB and stillbirth, when exposed to PM2/5 during gestation.
It also found that black mothers are at greater risk for PTB and LBW from social determinants of health, including urban residence and long-term, high-stress environments.
Studies on air pollution and LBW found associations in 19 states in the Northeast (10), Southeast (5), Midwest (2), Mountain (1), and West (1) regions. California had the greatest number of positive associations (13), followed by Massachusetts (6), Georgia (5), and Florida (4).
The study’s authors say that ob/gyns can take action beyond practice. “Physicians can adopt a more active role as patient advocates to educate elected officials entrusted with public policy and insist on effective action to stop the climate crisis,” they wrote.