Can obesity during pregnancy cause miscarriage or birth defects?

Miscarriage can occur in any pregnancy, and in every pregnancy, a woman starts out with a 3-5% chance of having a baby with a birth defect. This is called her background risk.
Maternal obesity has been associated with a higher chance for miscarriage and with a higher chance for certain birth defects, such as problems with the heart and spine. However, the overall increased risk for miscarriage and/or birth defects is likely to be small.