Maternal obesity and risk of Down syndrome in the offspring

The objective of this article is to determine if maternal obesity is associated with an increased risk of Down syndrome in the offspring and whether the risk estimates for trisomy 21 based on combined screening is affected by maternal body mass index (BMI).

Study group I consisted of a nationwide cohort of 1 568 604 women giving birth; outcome was infants born with Down syndrome [Correction made here after initial online publication.]. Adjustment was made for maternal age. Study group II consisted of 10 224 women undergoing 1st trimester combined screening. Outcome was risk assessment for Down syndrome. All women were divided into six BMI groups, and outcomes were evaluated over the BMI strata with BMI 18.5 to 24.9 as reference and correcting for maternal age.

Obese women had an increased risk for giving birth to an infant with Down syndrome compared with normal-weight women, BMI 30 to 34.9 odds ratio (OR) 1.31 [95% confidence interval (CI) 1.10-1.55], BMI 35 to 39.9 OR 1.12 (95% CI 0.82-1.53), BMI ≥ 40 OR 1.56 (95% CI 1.00-2.43). The observed and the expected numbers of women with a risk of Down syndrome >1/300 based on 1st trimester combined screen and maternal age were similar in each BMI group.

Maternal obesity seems to increase the risk for Down syndrome births. The risk estimate for Down syndrome with 1st trimester combined screening is unaffected by BMI.