Body mass index and birth defects: Texas, 2005-2008

Texas ranks 12th nationally in the proportion of adult residents who are obese; approximately 67 % of Texans are overweight or obese. Studies indicate that obesity is related to an increased risk for birth defects; however, small sample sizes have limited the scope of birth defects investigated, and only four levels of body mass index (BMI) are typically explored. Using six BMI levels, we evaluated the association between maternal BMI and birth defects in a population-based registry covering ~1.6 million births. Texas birth defect cases were linked to 2005-2008 vital records. Maternal BMI was calculated using self-reported prepregnancy weight and height from the vital record and categorized as follows: underweight (BMI <18.5), normal weight (BMI 18.5-24.9), overweight (BMI 25-29.9), class I obese (BMI 30-34.9), class II obese (BMI 35-39.9) and class III obese (BMI ≥40). Prevalence ratios for specific birth defects for maternal BMI categories were estimated by using normal weight as the referent, adjusted for maternal age and race/ethnicity, and stratified by maternal diabetes status. Risk for certain birth defects increased with increasing BMI (i.e., atrial and ventricular septal defects, pulmonary valve atresia, patent ductus arteriosus, and clubfoot). Risk for birth defects was substantially increased among some obese mothers (BMI ≥30) (e.g., spina bifida, tetralogy of Fallot, cleft lip with or without cleft palate, hypospadias, and epispadias). Conversely, mothers with higher BMI had a lower risk for having an infant or fetus with gastroschisis (aPR = 0.35; 95 % CI = 0.12, 0.80). Given the increased risk for birth defects associated with obesity, preconception counseling should emphasize the importance of maintaining normal weight.