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.