Both overweight and underweight women may be more likely to die in childbirth, a new study in JAMA suggests. This may explain why disturbing data from the Centers for Disease Control and Prevention suggests that the number of U.S. women who die in childbirth has doubled since 1987—while maternal mortality rates in countries with healthier diets have steadily declined.
“Today’s population of childbearing women have a higher proportion of obese women, older women, and women with chronic conditions including diabetes and hypertension,” study co-author Sarka Lisonkova of the University of British Columbia, told Fatherly. These factors are all known to contribute to complications and, occasionally, death among pregnant women.
Nearly half of U.S. women are overweight or obese during their first pregnancies. Prior studies have shown that these overweight and obese mothers may increase their babies’ risk of birth defects and heart disease, and may set up their offspring for a lifetime of struggling with obesity and diabetes. But this study is among the first to examine how a mother’s weight impacts her odds of dying in childbirth, and the first to conclude that being underweight is similarly dangerous.
For the study, Lisonkova and colleagues analyzed the body-mass index of 743,630 women who gave birth in Washington State between 2004 and 2013. Deaths and complications were rare, but results indicated a small increased risk for women who were overweight or underweight prior to getting pregnant. Specifically the risks of severe maternal illness or death were 0.288 percent higher for underweight women (BMI less than 18.5), 0.176 percent higher for overweight women (BMI 25.0-29.9), 0.249 percent higher for obese women (BMI of 30.0-34.9), 0.358 percent higher for obese women (BMI of 35.0-39.9), and 0.611 percent higher for obese women with a BMI of 40 or greater.
While the risk is greatest for women with the highest BMIs, Lisonkova was surprised to discover that underweight women were also at increased risk. Her findings underscore the important of maintaining a healthy weight throughout pregnancy—ideally between a BMI of 18.5 and 24.9.
Though the results build on past research, Lisonkova is careful to note that this is by no means the answer as to why maternal mortality rates are so high in the U.S. For one, there were not enough fatalities in the sample (0.oo4 percent to .012 percent of women) to rise to statistical significance. Lisonkova recommends researchers look at higher risk pregnancies, such as multifetal births, to come up with larger samples. (All of the mothers in this study were pregnant with one baby.)
Instead, Lisonkova says that the main takeaway is that mothers need to work hard throughout pregnancy to take care of themselves and maintain a healthy body weight, even when it’s difficult. “We all know that healthy diet and physical exercise are effective,” Lisonkova says. “However, that knowledge does not easily translate to a healthy lifestyle on a population level.”