Pregnant people in the United States who are exposed to air pollution and heat exposure have significantly higher chances of having a pre-term birth, stillbirth, or a baby with low birth weight, according to a new study. Black people and those with asthma are particularly at risk.

The report, “Association of Air Pollution and Heat Exposure With Preterm Birth, Low Birth Weight, and Stillbirth in the US: A Systematic Review,” was published on June 18 in the Journal of the American Medical Association. It looked at 57 past studies that made a connection between these environmental factors and negative pregnancy outcomes. Reports The Guardian:

In the review, 19 studies linked air pollution to pre-term birth, defined as a baby born alive before 37 weeks of pregnancy. Twenty-five studies linked air pollution to low birth weight. And four studies linked air pollution to stillbirth. One study found the risk of stillbirth increased 42 percent with high third-trimester exposure. Stillbirth is rare, so data on it is limited and it is difficult to draw broad conclusions about why it happens, [study co-author and retired obstetrician Bruce] Bekkar said.

Because poverty, long-term stress levels and access to healthcare—the social determinants of health—impact people of color more than Whites, the study concluded that Black mothers are at greater risk for pre-term birth and low birth weight.

These findings support the assertion by The American College of Obstetricians and Gynecologists that climate change is a grave threat to women’s health, with pregnant people and their fetuses especially vulnerable.

The study’s authors say that there are certain things that pregnant individuals can do to reduce their risk, such as be in air conditioning when possible during warm weather months. Yet, Bekkar stresses that the responsibility for change is not on individuals but policymakers. In an interview with The Guardian, he urges women’s rights advocates to pressure legislators, saying:

“We are already having generations weakened from birth. There’s just no way we can allow that to happen, and I would like to see not just mothers and their husbands and kids show up at council meetings, but I’d like to see many more health professionals involved in calling for legislation that reduces the ongoing and really pretty scary health burdens of the climate crisis.”

Read the entire study here.