Women who are obese before becoming pregnant are at an increased risk giving birth to babies born with birth defects, finds a study in Archives of Pediatrics & Adolescent Medicine.
Overweight and obese women are already known to be at risk for infertility, irregular menstruation and complications during pregnancy. But this latest study suggests their children could be at risk of life-threatening problems.
Dr. D. Kim Waller at the University of Texas in Houston and colleagues looked at the ongoing National Birth Defects Prevention Study, pulling data on over 10,000 babies born with birth defects between 1997 and 2002 and compared them with some 4,000 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.
For mothers who were overweight but not classified as obese, there was also a significant, but smaller, association with some of these defects.
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."
The authors concede that the reasons why maternal obesity would lead to structural birth defects are unknown. Waller says it's possible some of the obese women had undiagnosed diabetes.
Women who have diabetes prior to becoming pregnant often have difficulty controlling their blood sugar and that can lead to an increased risk of a range of birth defects. A similar mechanism could be causing birth defects in obese pregnant women.
It's also possible that some women tried potentially dangerous weight-loss diets before conception or during early pregnancy, when most birth defects occur.
Waller notes that the absolute risk of obese women having a child with a birth defect is still low. Nevertheless, she says the study's findings underline yet another reason for women to maintain a healthy weight.
She also cautions overweight women against dieting during pregnancy.
Health Canada recommends that women who were overweight before pregnancy should aim to gain 7 to 11.5 kilograms (15 to 25 pounds) during their pregnancy, rather than the 11.5 to 16 kilogram (25 to 35 pounds) weight gain recommended to women of a healthy weight.
