Impact of maternal body mass index on the antenatal detection of congenital anomalies

Objective: To investigate the association between maternal body mass index (BMI) and antenatal ultrasound detection of congenital anomalies.

Design: Population-based register study.

Setting: North of England (UK).

Population: All pregnancies (n = 3096) associated with a congenital anomaly notified to the Northern Congenital Abnormality Survey (NorCAS) during 2006-2009. Cases with chromosomal and teratogenic anomalies (n = 611) or without information on antenatal scanning (n = 4) were excluded.

Methods: Adjusted odds ratios (aORs) and 95% confidence intervals (CIs) for antenatal detection according to maternal BMI categories were estimated using logistic regression.

Main outcome measures: For all anomalies combined, cases were defined as 'detected' if any congenital anomaly was suspected antenatally. Organ system-specific anomalies were defined as detected if an anomaly of the correct system was suspected.

Results: Antenatal detection of any anomaly occurred in 1146 of 2483 (46.2%) cases with normal karyotype. The odds of detection were significantly decreased in obese (BMI ≥ 30 kg/m(2)) women compared with women of recommended BMI (18.5-24.9 kg/m(2); aOR, 0.77; 95% CI, 0.60-0.99; P = 0.046). Cardiovascular system anomalies were suspected antenatally in 109 of 945 (11.5%) cases. The odds of detecting a cardiovascular anomaly were significantly greater in underweight women (BMI < 18.5 kg/m(2)) than in women of recommended BMI (aOR, 2.95; 95% CI, 1.13-7.70; P = 0.027). There was no association between BMI and detection in any other organ system or between BMI and termination of pregnancy for fetal anomaly.

Conclusions: Antenatal ultrasound detection of a congenital anomaly is decreased in obese pregnant women. This has implications for the scanning and counselling of obese women.