NEW YORK (Reuters Health) - There's an increased risk of birth defects among babies born to women who are obese before becoming pregnant, according to a new study.

To look into this issue, Dr. D. Kim Waller and colleagues used information from the ongoing National Birth Defects Prevention Study, a multi-site, population-based study of more than 30 different categories of structural birth defects.

Waller, at the University of Texas in Houston, and associates pulled data for births between 1997 and 2002 on over 10,000 babies born with birth defects and compared them with some 4000 normal babies.

The team found that maternal obesity more than doubled the likelihood that the baby would have spina bifida. Other increased risks linked to the mother's pre-pregnancy obesity were defects involving the heart, anus, penis, limbs, diaphragm and navel, the researchers report in the Archives of Pediatrics and Adolescent Medicine.

For mothers who were overweight but not classified as obese, there was also a significant, but smaller, association with some of these defects.

Among underweight women, the only defect linked to their weight was a slightly increased risk of cleft lip.

Waller and colleagues conclude: "Our study supports previous evidence as well as provides new evidence for the associations between maternal obesity and particular categories of birth defects."