Climate change may cause pregnant women to have premature or stillborn babies, black mothers most at risk: Study
The review analyzed over 32 million births across 68 studies, of which 84% found a significant association of air pollutants and heat exposure with adverse birth outcomes
Pregnant women who are exposed to air pollution and high temperatures as a result of climate change are more likely to have babies who are premature, underweight or stillborn, with black mothers and their infants most at risk. The systematic review focuses on studies involving more than 32 million births in the US — the largest study to date and with an exclusive focus on the US population. The researchers assessed the associations between exposure to PM2.5, ozone, and heat and preterm birth, low birth weight, and stillbirth. A total of 57 studies (84%) found air pollution and heat to be risk factors. The analysis shows that 48 of 58 or 84% on air pollutants and 9 of 10 (90%) on heat showed a significant association of air pollutants and heat exposure with adverse birth outcomes. In the review, exposure to PM2.5 or ozone was associated with an increased risk of preterm birth (defined as a baby born alive before 37 weeks of pregnancy) in 19 of 24 studies (79%) and low birth weight in 25 of 29 studies (86%).
“This review suggests that increasingly common environmental exposures exacerbated by climate change are significantly associated with serious adverse pregnancy outcomes across the US. It appears that the medical community at large and women’s health clinicians, in particular, should take note of the emerging data and become facile in both communicating these risks with patients and integrating them into plans for care,” says the research team in their findings published in JAMA Network Open. It includes experts from Southern California Permanente Medical Group, San Diego; University of Texas McGovern Medical School, Houston; and California Office of Environmental Health Hazard Assessment, Air and Climate Epidemiology Section, Oakland, among others. They add, “Moreover, 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.”
Among racial/ethnic groups, the findings suggest that black mothers are at greater risk for preterm birth and low birth weight. “Social determinants of health, including residence in urban areas with higher exposure to air pollutants and long-term high levels of stress, are known to contribute to adverse obstetrical outcomes,” the authors write.
The review included studies that were published between January 1, 2007, and April 30, 2019. A total of 1,851 articles matched the search terms, of which 68 articles met the study criteria: 58 (85%) on-air pollutants and 10 (15%) on heat. A total of 32,798,152 births were analyzed, with a mean of 565,485 births per study. “Regarding exposure to PM2.5 and ozone, there were 24 (41%) studies on preterm birth, 29 (50%) on low birth weight, and 5 (9%) on stillbirth. Of the 58 studies addressing air pollution, 56 (96%) included PM2.5, 23 (40%) included ozone, and 21 (36%) analyzed both. Of these, 48 studies (84%) found a significant association between exposure to air pollutants and adverse birth outcomes,” says the team.
They found 10 studies examining the association between heat exposure and obstetrical outcomes: 5 (50%) on preterm birth, 3 (30%) on low birth weight, and 2 (20%) on stillbirth. Nine of the 10 articles (90%) found a significant association between exposure to heat during pregnancy and adverse birth outcomes. The analysis shows that of the 11 studies analyzing PM2.5 and exposure during pregnancy, the risk increased by an average of 11.5%. For example, in a study of traffic-generated PM2.5 in Los Angeles and Orange County, California, experts found that that preterm birth overall increased 3%, deliveries less than 35 weeks increased 7%, and deliveries less than 30 weeks increased 18%. Of the 4 studies analyzing ozone and exposure during pregnancy, 2 (50%) found an increased risk from 3% to 9.6%
10 studies reported the association of racial/ethnic disparities with increased risk of preterm birth among mothers in minority groups; 8 of the studies noted higher risk for black mothers, which was the most consistent finding among the subgroups. One study analyzing subgroups revealed a higher risk of preterm birth among patients with asthma. Of the 29 studies evaluating the association of maternal exposure to PM2.5 and/or ozone with low birth weight, with 25 studies reporting an increased risk. Eight studies that analyzed pregnancy exposure to PM2.5 found a 2% to 36% increased risk of low birth weight. One study from Florida, for example, reported a 3% increased risk of low birth weight for each 5 km nearer residential proximity to a solid waste plant emitting PM2.5. Again, 3 studies found that exposure to ozone was associated with a significant increase in the risk of low birth weight, with two noting a 6% to 13% increased risk. Most of the studies that examined the link between air pollution and low birth weight found that the risks were greater for black mothers. “As with preterm birth and air pollutants, the most frequently noted high-risk subpopulation was black mothers in 10 of 13 studies (77%); 4 (31%) noted higher risks among Asians, and 3 (23%) among Hispanics,” the findings state.
Limited studies were identified for stillbirth because of the lack of available data for health studies. Five studies examined the association of maternal exposure to PM2.5 and/or ozone with stillbirth and four found an increased risk. “For PM2.5, a study of more than 350,000 births in Ohio noted an increased risk (42%) of stillbirth associated with high exposure during the third trimester. The studies of prenatal ozone exposure either during the whole pregnancy, the third trimester, or the week before delivery identified a range of increased risk of stillbirth from 3% to 39%,” the authors write. Further, two studies noted subpopulations at higher risk: mothers with asthma and Hispanic mothers. An analysis of 12 clinical sites across the US, for example, found that mothers with asthma were especially susceptible to a stillbirth if exposed to elevated PM2.5 throughout their pregnancy.
Among five studies evaluating the association of maternal exposure to heat with preterm birth, a total of 4 (80%) found an increased risk. They identified a range of increased risk of preterm birth from 8.6% to 21%. Three studies examining large numbers of preterm births in California noted an increased risk of preterm birth for each 5.6°C-increase in temperature, as did another study covering 12 clinical sites across the US for 2.8°C increase. Two reports from California found an association of racial/ethnic disparity and heat exposure with an increasing risk of preterm birth; higher risk was found among black mothers.
“Regarding both air pollutants and heat exposure, associations with adverse birth outcomes were found across the continental US. For example, studies on air pollution and low birth weight found an association in 19 states in the Northeast (10), Southeast (5), Midwest (2), Mountain (1), and West (1) regions. California, known for both high temperatures and unhealthy \ particulate and ozone levels, was included in the greatest number of studies showing a positive association (13), followed by Massachusetts (6), Georgia (5), and Florida (4),” says the team. They add, “The exposures are complex. Even within 1 state, the weather patterns, geography, and urbanization may create zones with widely different pollution risks.”
In a related commentary, Dr Linda C Giudice from the Department of Obstetrics, Gynecology and Reproductive Sciences, University of California, says that since direct control over climate is often beyond the control of an individual, advocacy for regulations to minimize these exposures is essential. “The time has come for us to come together to protect the health of all global citizens, especially women and children, from the consequences of climate change now and in the years ahead. There is just too much at stake to take an alternative path,” says Dr Giudice.