Maternal Obesity Heightens Risk of Birth Defects

U.S Department of Health & Human Services, Oct 25, 2007

Women who were obese before they became pregnant had a higher risk of having babies with certain birth defects, including missing limbs, malformed hearts and underdeveloped spinal cords, a new study found. But the researchers cautioned that overweight women planning to get pregnant should try to lose weight sensibly and carefully.

"We would advise women who are obese to try to maintain a healthy weight, engage in moderate exercise and follow a healthy daily diet," said study lead author Kim Waller, associate professor of epidemiology at the University of Texas at Houston's School of Public Health. "Multivitamins both before and after a woman becomes pregnant are very important."

In particular, women are advised to take 400 micrograms of folic acid daily both before pregnancy and during pregnancy. A multivitamin will usually satisfy this recommendation. And women should not try fad diets.

"We don't want women who are thinking of becoming pregnant or who are pregnant to rush out and go on a crash diet," Waller cautioned. "If you become pregnant, then, sure, maybe try to lose some weight, but do so very, very carefully and maintain a healthy diet while you're doing so."

"You have to be of a healthy weight not only for yourself but also for a healthy pregnancy," added Dr. Jennifer Wu, an obstetrician/gynecologist at Lenox Hill Hospital in New York City. "You want to try to get down to a healthy weight before you even get pregnant in the first place. Pregnancy is not the time to do a crash diet to try to lose weight."

In 2003 and 2004, 51 percent of U.S. women aged 20 to 39 were overweight or obese, putting them at increased risk for chronic diseases, infertility, irregular menstruation and pregnancy complications, according to background information in the study. Previous research had shown a strong association between pre-pregnancy body mass index (BMI, a ratio of weight to height) and the risk for certain birth defects, particularly anencephaly -- a defect in the closure of the neural tube, which forms the brain and spinal cord of the embryo -- and spina bifida. The link between overweight and obesity and other birth defects has been less clear. According to the U.S. Agency for Healthcare Research and Quality, as many as one in 33 babies born in the United States has a birth defect.

For the new study, the largest of its kind, Waller and her colleagues interviewed 10,249 women in eight states whose babies had been born with birth defects between 1997 and 2002. Information on the women came from the National Birth Defects Prevention Study. These women were then compared to 4,065 women who had given birth to babies without birth defects during the same time period. Sixteen birth defects were studied. Of those, mothers of babies with the following seven birth defects were more likely to have been obese than mothers of infants without birth defects:

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