Maternal Obesity Heightens Risk of Birth Defects

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:

Spina bifida, or the incomplete development of the brain, spinal cord and/or meninges (the protective covering around the brain and spinal cord). This is the most common neural tube defect in the United States and affects up to 2,000 of the more than 4 million babies born annually, according to the National Institutes of Health. Heart defects. Anorectal atresia, or malformation of the anal opening.Hypospadias, or an abnormally placed urethral opening in males -- on the underside instead of the end of the penis. Limb reduction defects, such as small or missing toes, fingers, arms or legs. Diaphragmatic hernia, an opening in the diaphragm that allows abdominal organs to move into the chest cavity. This may also cause lungs to be underdeveloped. Omphalocele, when the intestines or other abdominal organs protrude through the navel.

The study authors noted that the overall risk of having a child with a birth defect related to obesity is low. And mothers of babies born with gastroschisis (when organs protrude through a defect in the abdominal wall other than the navel) werelesslikely to be obese than mothers of babies without birth defects.

The findings are published in the August issue ofArchives of Pediatrics & Adolescent Medicine.

It's not clear why the association between pre-pregnancy obesity and birth defects exists.

"We know that obese women have a higher risk of certain defects, but we don't know if obesity is the direct cause," Waller said. "There could be other explanations, such as different types of diet, different ways of dieting when they're dieting. We were not able to exclude women with diabetes, and that is a very strong risk factor for birth defects, so we think there may be undiagnosed cases of diabetes remaining with the study."

Future research will look at dieting techniques and the risk of birth defects, as well as any links between over-the-counter diuretics and appetite suppressants and birth defects.

More information

Find out more about a healthy pregnancy at the U.S. Centers for Disease Control and Prevention.

SOURCES: Kim Waller, Ph.D., associate professor of epidemiology, School of Public Health, University of Texas, Houston; Jennifer Wu, M.D., obstetrician/gynecologist, Lenox Hill Hospital, New York City; August 2007,Archives of Pediatrics & Adolescent Medicine