Maternal obesity and morbid obesity: the risk for birth defects in the offspring

The objective of this study was to assess, in a large data set from Swedish Medical Health Registries, whether maternal obesity and maternal morbid obesity were associated with an increased risk for various structural birth defects.

The study population consisted of 1,049,582 infants born in Sweden from January 1, 1995, through December 31, 2007, with known maternal weight and height data. Women were grouped in six categories of body mass index (BMI) according to World Health Organization classification. Infants with congenital birth defects were identified from three sources: the Swedish Medical Birth Registry, the Register of Birth Defects, and the National Patient Register. Maternal age, parity, smoking, and year of birth were thought to be potential confounders and were included as covariates in the adjusted odds ratio analyses.

Ten percent of the study population was obese. Morbid obesity (BMI > or = 40) occurred in 0.7%. The prevalence of congenital malformations was 4.7%, and the prevalence of relatively severe malformations was 3.2%. Maternal prepregnancy morbid obesity was associated with neural tube defects OR 4.08 (95% CI 1.87-7.75), cardiac defects OR 1.49 (95% CI 1.24-1.80), and orofacial clefts OR 1.90 (95% CI 1.27-2.86). Maternal obesity (BMI > or = 30) significantly increased the risk of hydrocephaly, anal atresia, hypospadias, cystic kidney, pes equinovarus, omphalocele, and diaphragmatic hernia.

The risk for a morbidly obese pregnant woman to have an infant with a congenital birth defect is small, but for society the association is important in the light of the ongoing obesity epidemic.