The Clean Air Act must protect pregnant women: here’s how

Whether at the Oscars or the March for Science, women are increasingly standing up with each other and questioning the status quo in everything from entertainment to politics, including in my field of environmental health.

Protecting women during pregnancy from pollution might seem like an obvious public health objective, yet in the 40-plus year history of the Clean Air Act – under Democratic and Republican administrations alike – the US Environmental Protection Agency (EPA) has not given any special protection to pregnant women although it has legal authority, and arguably the duty, to do so.

Air pollution is associated with heart disease which can appear in women first during pregnancy, but women — and pregnant women in particular — are an under-studied group with respect to cardiovascular disease.  With air pollution, like particulate matter and ozone, we often worry about protecting children, but what about protecting mom?

In a paper published in World Medical and Health Policy in March 2018, my co-authors and I examined to what extent  Clean Air Act national ambient air quality standards consider pregnant women. A key finding of our paper is that pregnant women must be considered an at-risk population and given protection when EPA is making a decision about air pollution standards that include margin of safety which is mandated by the Clean Air Act. Our recommendation is consistent with statements from medical societies including the American College of Obstetrics and Gynecology, the American Heart Association, and the American Thoracic Society.

By law, the EPA Administrator considers three factors in setting standards: the nature and severity of the effects; the uncertainties in the data; and the size of the at-risk populations. How does EPA identify who is at risk? Currently, EPA starts with a health outcome and then backs out the group experiencing the effect. But this is antithetical to the preventative goals of the Clean Air Act and isn’t practical for an especially vulnerable group like pregnant women for whom ethical considerations would preclude some of the types of studies EPA’s procedures require. It’s a Catch-22; pregnant women would have to experience harm from air pollution before EPA would prevent the harm. To move beyond this flawed approach, we argue for the routine inclusion of pregnant women as an at-risk population.


First, the science supports the inclusion of pregnant women as an at-risk population under the Clean Air Act.  During pregnancy, women’s breathing volume increases by 40% to accommodate the demands of pregnancy and oxygen transfer across the placenta. Thus, pregnant women breathe in more pollutants than other adults. These natural compensatory changes that occur to the cardiopulmonary system during pregnancy are essential to maintaining the pregnancy, but these same adaptations may also render pregnant women more susceptible to additional health challenges, like air pollution exposure, which increases risk of adverse cardiovascular effects, contributing to poor health outcomes during pregnancy and beyond. In addition, pregnant women experience sensitive maternal exposure periods (e.g., during conception, placenta implantation, artery remodeling, and labor). Furthermore, air pollution is also associated with health problems only found among pregnant women (e.g., preeclampsia, gestational hypertension, and gestational diabetes). In setting air pollution standards, a risk assessment that specifically examines the effect on pregnant women is warranted.

Second, protection of pregnant women under the Clean Air Act would protect communities with the worst problems.  Nationally, disparities have been documented regarding exposure to air pollution among pregnant women by race/ethnicity, education, and income.  Women with preexisting conditions, women experiencing poverty, and groups that suffer systematic discrimination are more susceptible to cardiac effects of air pollutants during pregnancy.

In our study, we rigorously reviewed 11 studies of more than 1.3 million pregnant women in the United States to characterize the relationship between air pollution and high blood pressure – an indicator of cardiovascular problems – and an additional social stressor, such as lack of education.  We concluded that adequate evidence associates exposure to particulate matter with an adverse effect of hypertensive disorders among pregnant women.

From a policy perspective, the legislative history of the Clean Air Act and US EPA’s regulatory practice endeavor to protect sensitive groups, leading to fuller risk reduction across the population, while acknowledging the standards are not intended to be risk-free. We have previously pointed out deficits in EPA’s process, which could begin by identifying vulnerable groups.

Relying solely on scientific air pollution studies to identify vulnerable populations is logically flawed.  Essentially, these groups must first experience and demonstrate harm before being afforded protection under the law. These procedures conflict with the statutory language in the Clean Air Act’s goal of preventing likely harms from air pollution exposure. Furthermore, some groups, like pregnant women, may be especially difficult to study and thus are under-represented in the literature.

EPA’s risk assessment techniques should be improved to consider the impact of air pollution exposure on pregnant women’s health. The existing Clean Air Act standards set without these considerations are inadequate. EPA is misidentifying and thus underestimating the size of the at-risk population. EPA has a duty to protect at-risk populations with an adequate margin of safety. It is finally time that EPA fully assesses the risk to pregnant women and act to protect them.