by Kristin Harmel
April 28, 2010

If you’re planning to get pregnant, trying to conceive, or expecting a baby, you may want to check in with your doctor about your weight to ensure you are in a healthy range. A new study published in the American Journal of Clinical Nutrition finds that maternal obesity may increase a baby’s risk of heart defect.

Researchers at the National Institutes of Health (NIH) and the New York State Department of Health found that on average, obesity increases a woman’s chance of having a baby with a heart defect by around 15 percent. As the mother’s level of obesity rises, so too does the child’s risk of heart problems. Women who are moderately obese (with a body mass index, or BMI, over 30) are 11 percent more likely to have a child with a heart defect, researchers say, while for morbidly obese women (with a BMI over 40), the risk jumps to 33 percent.

“The current findings strongly suggest that by losing weight before they become pregnant, obese women may reduce the chances that their infants will be born with heart defects,” says Alan E. Guttmacher, M.D., acting director of the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), in a press release.

According to the NIH, heart defects affect 8 in every 1,000 newborns, making them the most common type of birth defect. Previous studies have also shown numerous other links between obesity and difficulties during pregnancy, including increased risk of hypertension, preeclampsia, gestational diabetes, and cesarean birth.

“The trend is unmistakable: the more obese a woman is, the more likely she is to have had a child with a heart defect,” says the study’s lead author, James L. Mills, M.D., M.S., from the NICHD’s Division of Epidemiology, Statistics and Prevention Research. “If a woman is obese, it makes sense for her to try to lose weight before becoming pregnant. Not only will weight loss improve her own health and that of her infant, it is likely to have the added benefit of reducing the infant’s risk for heart defects.”