Infants born to obese mothers are a third more likely to suffer significant birth defects, including spina bifida, heart defects and at least five others, according to a study released today.
The study, published in the journal Archives of Pediatrics and Adolescent Medicine, found the risk for spina bifida, a disorder in which the spinal cord is incompletely formed, more than doubled, while that for omphalocele, a condition in which the intestines or other abdominal organs protrude from the belly button, increased 63%.
About 4% of infants born to obese mothers had significant birth defects, compared with 3% for infants born to all women, said senior author Kim Waller, an epidemiologist at the University of Texas at Houston Health Science Center School of Public Health.
"This is another important reason for women to maintain a healthy weight," she said, as more than 50% of women age 20 to 39 are overweight or obese.
For unknown reasons, the risk for gastroschisis -- similar to omphalocele but the organs develop outside of the abdomen -- decreased by 81% for infants born to obese mothers.
The latest study used information on more than 10,000 mothers whose babies had birth defects and about 4,000 mothers whose babies did not.
The team, from Texas, California, Georgia, Arkansas and North Carolina, used data from the National Birth Defects Prevention Study, which has been collecting information since 1997.
Previous studies had associated maternal obesity with an increased risk of heart defects and spina bifida.
In the new study, Waller wanted to look at a broader range of defects across a larger group of subjects.
Only birth defects with more than 150 cases were included, and mothers who had diabetes and infants with birth defects caused by single-gene or chromosomal abnormalities were excluded.
The researchers related the birth defects found in the study with the body mass index of mothers. The index reflects the ratio of height to weight; a person with a BMI of 30 or higher is considered obese. A 5-foot-6 woman weighing 186 pounds would have a BMI of 30.
The study looked at 16 birth defects and found a link between maternal obesity and an increased risk for seven of them.
In addition to spina bifida and omphalocele, the study's findings included a 36% increased risk for small or missing limbs, a 40% increased risk for heart defects and a 46% increased risk for anorectal malformation.
Waller said the study did not look at how obesity was related to the defects. It may be that obesity does not cause the defects but is a marker for other factors that do.
She said one possibility was that the obese mothers had undiagnosed Type 2 diabetes.
"Diabetes is a strong and well-known risk factor for birth defects, and obese women are more likely to get diabetes," she said.
Other explanations include differences in the types of food obese women eat or the potential effect of weight-loss techniques, such as fasting or diet modifications.
All women should eat a healthy diet with fortified foods and take a folic acid supplement before and during pregnancy, Waller said.