Extreme summer heat is miserable for all of us, but new research is finding it may be especially dangerous for pregnant women who face an increased risk of miscarriage during peak summer months.
A research team led by Amelia Wesselink, PhD, assistant professor of epidemiology at Boston University School of Public Health, found that pregnant women have a 44% higher risk of miscarriage in August than in February, the month with the lowest rate of miscarriage. Heat is thought to be behind this finding, but researchers plan to dig deeper into potential causes.
In their study, Wesselink and her team analyzed pregnancy outcomes for more than 12,000 women across different seasons. Miscarriage rates were highest in peak summer—late August—especially for women in some of the hottest areas of the country, the southern and midwestern U.S.
Between 2013 and 2020, data were collected on American and Canadian pregnant women enrolled in the Pregnancy Study Online (PRESTO), an internet-based fertility study from Boston University School of Public Health. Each study participant was followed for up to one year after enrollment. Researchers looked at participants’ income, education, race, ethnicity, lifestyle, and responses to follow-up questions about their pregnancy and miscarriage. Women seeking fertility treatments were not included in the study.
Most of the women in the study were white (86%), had at least a college degree (79%), and many earned more than $100,000 a year (47%). Half of the women were able to conceive within a year of planning to get pregnant. Of the women who did conceive, nearly 20% of them miscarried.
The risk of miscarriage was 44% higher in August for pregnancies in their first 8 weeks and 31% higher for pregnancies at any point.
Saifuddin Ahmed, PhD, a researcher at Johns Hopkins Bloomberg School of Public Health in Baltimore, stated extreme heat may not be the only thing to blame for this observation. “You need to be careful when linking summer months to miscarriage, as women may pursue more outdoor activities during summer.”
Wesselink also noted that study participants were not representative of the general population—most were white and wealthier than average.
Sources: Epidemiology, Medscape