Aside from being hot, sweaty, and uncomfortable, there’s one more thing expecting mothers need to worry about in the summer: Pregnant women are 27 percent more likely to go into early-term labor during periods of extreme heat, according to a new study from the University of Montreal.
Researchers analyzed data from over 219,000 births over 29 years. They looked at the maximum daily temperatures in the week preceding the birth, and the number of consecutive days with temperatures at or above 89 degrees during the preceding week.
Here’s what they found: When maximum temperatures were at least 89 degrees for four to seven days, women were 27 percent more likely to have early-term births, or births from 37-38 weeks (full-term births are characterized as 39 weeks or later). Essentially, heat shortened the delivery time slightly, says lead study author Nathalie Auger, M.D., of the University of Montreal
The researchers believe there may be a few reasons for these findings. The first is that heat could increase contractions. Another theory is that sensitivity to heat is simply greater the farther along you are, because thermoregulation—your body's ability to control its temps—may be less efficient. Another factor could be dehydration, which can reduce uterine blood flow and increase the excretion of your pituitary hormones, which may induce labor.
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While it's certainly possible to still have a healthy birth at 37 or 38 weeks, one study in JAMA Pediatrics found that babies born early-term were at a higher risk for adverse outcomes, such as the need for respiratory support or admission to the neonatal intensive care unit.
Although you can't exactly control the weather, the researchers advise staying out of the heat and in the air conditioning if there's a heat wave within a few weeks of your due date. If you know you'll be outside, stay well hydrated and take frequent breaks in the AC. For more baby bump advice, check out our tips for a happy, healthy pregnancy.