It involves a review of 39 studies in the Journal of the American Medical Association.
The report finds obese women have a 30-percent higher risk of birth defects including twice the risk of spina bifida and a 20 percent increased risk of cleft lip and palate.
Researchers suspect this has to do with higher insulin levels in the mother's body.
The risk for any one baby is small but as obesity levels continue to climb, researchers say the overall rate of birth defects could increase.
The study also adds to the evidence that pregnant women carrying too much weight increase their risk of diabetes, high blood pressure as well as blood clots.
