Maternal obesity and detection rate of fetal structural anomalies

To estimate the effects of maternal body mass index (BMI) on the sensitivity of detecting fetal anomalies by a routine ultrasound performed either in the first or in the second trimester.

Unselected pregnant women (n = 19,140) were divided into four BMI groups: underweight (<18.5), normal weight (18.5-24.9, reference group), overweight (25.0-29.9), and obese (≥30.0). Fetal anomaly diagnoses were grouped according to their likely clinical consequences as suggested by the Royal College of Obstetricians and Gynaecologists. Minor anomalies were excluded. The detection rate of fetal anomalies in each BMI group was calculated and compared.

The prevalence of infants with structural anomalies in the study population was 4% and the prevalence of material obesity was 10%. The detection rates of fetal structural anomalies were 26% for normal-weight, 29% for overweight (odds ratio (OR) 1.15, 95% confidence interval (CI) 0.68-1.95), and 19% for obese women (OR 0.67, 95% CI 0.29-1.52). The detection rate of anomalies with long-term handicap was lower in the obese group (27.3%; OR 0.44, 95% CI 0.11-1.79) compared to normal-weight women (46.3%).

The detection rate of fetal anomalies seems to be lower for obese women, but these findings need to be further investigated.