Global Warming Might Be Especially Dangerous for Pregnant Women

Ellie Kincaid Nov 21, 2017

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A handful of researchers in the United States, Canada, and elsewhere are methodically accumulating evidence suggesting that higher temperatures could be linked to a higher risk of premature births, stillbirths, or other negative pregnancy outcomes. The findings in each case, while compelling, still raise as many questions as they seem to answer, and all the researchers say that much more work needs to be done. But they also suggest that enough evidence has already surfaced to warrant increased scrutiny—particularly as global warming is expected to drive average temperatures ever upward over coming decades.

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Her research suggested that an increase of 10 degrees Fahrenheit in weekly average “apparent” temperatures—a combination of heat and humidity—corresponded to an 8.6 percent increase in premature births. That association was independent of air pollution.

Later, she turned her attention to stillbirths, doing a similar temperature analysis with a state registry of fetal death certificates. In March of 2016, Basu published the results from analyzing more than 8,500 stillbirths that occurred during a decade of California’s warm seasons: Stillbirth risk was 10.4 percent higher with a 10-degree Fahrenheit apparent-temperature increase.

After her research on premature birth, the stillbirth results were “pretty much on par with what I was expecting,” Basu said. “I would be shocked if there wasn’t an association.”

These findings have been echoed independently elsewhere. Looking at records of more than 5,000 stillbirths in Quebec over 30 years, Nathalie Auger of Quebec’s institute for public health found that with higher temperatures, stillbirth risk increased continuously for certain categories of stillbirths. For those considered full-term, happening after 37 weeks of pregnancy, the odds of stillbirth were 16 percent higher at 28 degrees Celsius (82 degrees Fahrenheit) compared to 20 degrees Celsius (68 degrees Fahrenheit). The increase in odds of stillbirths between those two temperatures was 19 percent for stillbirths where the cause was marked in the registry as unknown, and 46 percent for those attributed to maternal complications.

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In addition to their case-crossover study, the group examined the effects of chronic exposure to heat through the whole course of a pregnancy, and were surprised to find the odds of stillbirth were 3.7 times greater when women experienced temperatures that were in the top 10 percent of the range for their location.

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