Sonja Rasmussen, from the US Centers for Disease Control & Prevention’s National Center on Birth Defects and Developmental Disabilities, and colleagues studied data collected on 6,440 infants with congenital heart defects, and 5,673 infants without birth defects, enrolled in the National Birth Defects Prevention Study (1997-2004).  The researchers also determined prepregnancy body mass index (BMI) of the mothers. Compared with women of normal weight at the beginning of pregnancy, the team found that overweight mothers were at 18% increased risk of giving birth to a child with congenital heart defects; the most severely obese mothers were at 30% increased risk.