Obesity Carries Pregnancy Risks
Obese Women More Likely to Have Babies With Birth Defects, Study Shows
Feb. 10, 2009 -- Women who are obese during pregnancy have a higher risk
than normal-weight women of having babies with certain birth defects, including
neural tube defects such as spina bifida, heart problems, and cleft palate and
lip, according to a new review.
"It is important to note that birth defects are a rare event and occur
in 2%-4% of pregnancies, so the risk remains very low," says Judith Rankin,
PhD, a study co-author and a reader in material and perinatal epidemiology at
the University of Newcastle in England. "The last thing we want to do is
Rather, the goal is to inform them, she says, and to encourage women who are
obese to get preconception counseling about weight loss.
The new report, published in this week's Journal of the American Medical
Association, is a review of previously published work. Rankin and her
colleagues culled the medical literature, pooled the results of 18 studies, and
reviewed the findings of 39 other studies to determine if the association
between obesity and birth defects still held up. It did.
Obesity & Birth Defects: The Study
Rankin's team undertook the study because of the growing problem of obesity
in women of childbearing age. In the U.S., one-third of women 15 and older are
obese, the authors note, and those numbers are expected to rise.
"This is a very important public health issue given the growing numbers
of women who are obese at the start of pregnancy," says Rankin, who notes
that obesity is also increasing in the U.K.
Obesity & Birth Defects: Results
In the new analysis, women who were obese before pregnancy or in early
pregnancy had a significantly increased risk of having a baby with birth
defects. The risks differed for specific problems.
- The risk of spina bifida was more than two times as high for obese pregnant
women, and the overall risk of neural tube defects was nearly twice as
- The risk of cardiovascular defects was 30% higher.
- The risk of cleft lip and cleft palate, either singly or together, was
about 20% higher.
- The risk of hydrocephaly (an abnormal buildup of fluid in the brain) was
- Limb reduction abnormalities were 30% higher.
The definitions of overweight and obese differed somewhat from study to
study, but many studies used those set by the World Health Organization -- a
body mass index or BMI of 25 and above for overweight and 30 and above for
More research is needed to determine if the link between excess weight and
birth defects holds for overweight women. "There isn't the same amount of
research evidence for overweight as there is for obesity,'' Rankin says.
Obesity & Birth Defects: Explaining the Link
Exactly how obesity increases birth defect risk isn't known, but the
researchers offer possible explanations.
- Because maternal diabetes is known to increase the risk of birth defects,
and obese women are at higher risk for type 2 diabetes, the mother-to-be may
have undiagnosed diabetes.
- Obese women have been shown to have nutritional deficiencies, especially
reduced levels of folate, which is important to prevent neural tube defects.
Obese women may need more than the amount routinely recommended to prevent