Mom's Obesity Raises Newborn's Heart Risk

The more obese a woman is when she becomes pregnant, the greater the likelihood that her newborn baby will have a congenital heart defect, a new study suggests. The finding raises concerns because 1 in 5 women are obese at the start of pregnancy in the United States.

Earlier studies have linked obesity during pregnancy to several health problems for both mothers and their offspring. Obesity increases the likelihood for pregnancy-induced hypertension, gestational diabetes, cesarean delivery and other complications. The newborns of obese moms are at increased risk for being overweight or developing type 2 diabetes later in life.

Some studies have also tied maternal obesity to different types of birth defects, including neural tube defects. But evidence has been inconsistent on the link between maternal obesity and congenital heart defects, the most common type of birth defect. Congenital heart defects—which affect 8 in 1,000 newborns—are problems with the heart's structure that are present at birth. They can range from minor to life threatening.

To help clarify the relationship between excess weight at the start of pregnancy and congenital heart defects, scientists from NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) and the New York State Department of Health analyzed data from the New York State Congenital Malformations Registry.

The researchers scanned through the records of over 1.5 million births that took place during an 11-year period. They compared about 7,000 women whose children were born with major heart defects to about 56,000 women whose offspring had no birth defects. The researchers calculated the mothers' body mass index (BMI), a ratio of weight to height. A normal BMI is 18.5 to 24.9; overweight is 25 to 29.9 and obese is 30 and above.

In the April 7, 2010, advance online edition of the American Journal of Clinical Nutrition, the scientists reported that the chance of having a child with a congenital heart defect increases for obese women, and rises sharply for morbidly obese women. While moderately obese women are 11% more likely than normal-weight women to have a child with a heart defect, morbidly obese women are 33% more likely. Women who were overweight but not obese had no increased risk.

Because the study examined the records of infants after birth, it couldn't address whether obese women who lose weight before they conceive can reduce their babies' risks of heart defects. However, the researchers say, the findings suggest that attaining a healthy weight before conception would reduce the risk for newborn heart defects.

"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 NICHD researcher Dr. James L. Mills, first author of the study. "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."