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High heat is not good for a developing baby during pregnancy. And neither is air pollution. A just published large study concluded that higher temperatures from climate change and increased air pollution (from ozone and fine particulates PM2.5) increases the risk of giving birth to premature, underweight, or stillborn children.

The researchers analyzed 68 studies, for a total of 32,798,152 births in the United States. Almost 33 million births! Another important finding was that those at highest risk were persons with asthma and minority groups, especially black mothers.

The researchers point out that animal studies find the same things: "that both air pollutant and heat exposure may contribute to adverse obstetrical outcomes". So there is lots of support for these findings of harmful effects.

Another recent study (by Univ. of California researchers) drew similar conclusions: that exposure to heatwaves during the week before birth was strongly linked to an increased risk of preterm delivery. And the hotter the temperature or the longer the heatwave, the greater the risk.

Since the long-term forecast is for increasing temperatures and longer duration heat waves throughout the world, these findings are very worrisome.

The study published in the JAMA Network Open (a Journal of the American Medical Association): Association of Air Pollution and Heat Exposure With Preterm Birth, Low Birth Weight, and Stillbirth in the USA: Systematic Review

A NY Times discussion of the findings: Climate Change Tied to Pregnancy Risks, Affecting Black Mothers Most

Discussion of earlier study (Feb. 2020) from Science Daily: Heatwave exposure linked to increased risk of preterm birth in California