Canadian researchers looked at the records of 219,319 live births in relation to temperature, and found that heat waves (defined as temperatures above 32 degrees C or 89.6 degrees F for four to seven days in a row) were associated with a 27 percent greater risk of an early-term pregnancy, compared to more moderate temps. Meaning, pregnant women exposed to extreme heat for an extended period of time were more likely to deliver at 37 and 38-weeks, as opposed to the usual 40.
"Pregnancy becomes more physically challenging as you get closer to term," says Nathalie Auger, MD, MSc, researcher at the University of Montreal's department of social and preventive medicine, and author of the study. Consider heat an added stressor on an already stressed body: "Physical stresses—like heat—have a greater impact at 37 or 38 weeks, than earlier in your pregnancy," says Dr. Auger.
While 37 weeks may seem close enough, those last few weeks in the womb are important to your baby's development. The brain, lungs and other organs are still maturing and preparing for life outside the womb.
Want to make sure you carry for the full term? Keep cool when the heat is on. Dr. Auger suggests the same tips that keep heat stroke at bay: drink water and stay in the shade or air-conditioning.
Note: You should never get to the point where you feel thirsty, a sign of dehydration. (Dehydration can also induce labor.)