Mother's Obesity Raises Risk of Birth Defects

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The health risks of being obese are certainly well known by now — diabetes, heart disease, stroke and hypertension, to name a few. But the dangers are even greater for pregnant women and particularly for their developing babies. A new analysis, published Feb. 11 in the Journal of the American Medical Association, documents a wider than expected range of birth defects that are more likely to plague babies born to obese women.

Led by Katherine Stothard at Newcastle University in Great Britain, the researchers reviewed 18 earlier studies of maternal weight and congenital abnormalities. Compared with women who maintained the recommended body mass index (BMI) of between 18.5 and 26, women who were obese — defined as having a BMI of 29 or greater — before pregnancy were more than twice as likely to have an infant with spina bifida, nearly twice as likely to have a baby with other neural-tube defects, and more vulnerable to giving birth to babies with heart problems, cleft palate or cleft lip, abnormal rectum or anus development, and hydrocephaly, a condition in which excess spinal fluid builds up in the brain. While the risk of birth defects in obese women has been known, "I wouldn't have predicted the range of birth defects found to be increased when we looked at maternal obesity," says Judith Rankin, an epidemiologist and one of the authors of the study. (See the best and worst moms of all time.)

Earlier studies, including surveys by the Centers for Disease Control and Prevention, had documented the greater risk of neural-tube defects and kidney problems in children of obese moms. But the new study serves as a warning to both doctors and patients that a mother-to-be's extra pounds should be considered a more powerful and far-reaching risk factor during pregnancy. While there are no conclusive explanations yet, researchers have three theories about why maternal obesity may lead to congenital abnormalities. First, many obese women may also have undiagnosed diabetes, which can lead to abnormal development of a fetus. Second, these moms may be eating a diet that is not as nutritionally sound as that of normal-weight women; obese women are more likely to be missing key nutrients, like folic acid, that are needed to prevent birth defects such as neural-tube abnormalities. "Levels of these nutrients might be lower in these moms, or if they are taking supplements, they may not be at levels that are adequate," says Dr. Sina Haeri, a fellow in maternal and fetal medicine at the University of North Carolina Chapel Hill, who authored a study on obesity in pregnant teens.

Finally, says Rankin, the issue may be one of screening: because ultrasound monitoring of obese patients is much more difficult than the monitoring of thinner women, it could lead to more missed cases of deformities like neural-tube defects. "We know that it is much harder to get good visibility of the fetus in scanning women who are obese, and more babies may be born with spina bifida and other abnormalities in these women," says Rankin. (Read "The Year in Medicine 2008: From A to Z.")

The study highlights the need for both doctors and patients to be aware of the added risk that maternal obesity places on the developing baby. Doctors should not only advise women who are planning a family to try to maintain their recommended weight, but also ensure that those who are already pregnant receive proper nutrition and thorough ultrasound screening. "It's important to remember that these adverse effects only affect a low percentage of obese women," says Rankin. "But there are certain things that could be put into place to protect women and their babies if they are thinking of having a family."

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