The influence of maternal body mass index on fetal anomaly screening

Abstract Objectives Maternal obesity is increasing and affects the quality of ultrasound images. The aim of this study was to examine the relationship between maternal body mass index (BMI) and requirement for repeat fetal anomaly scans and to determine whether gestational age at the initial scan affects the completion rate. Study design This was a retrospective cohort study of BMI and ultrasound scan data from 1000 women with singleton pregnancies delivering over a two month-period in a tertiary obstetric unit. Statistical analysis was used to determine the correlation between BMI and number of scans for completion and between gestational age and number of scans for completion. Women were classified into four groups according to BMI for comparison of the need for repeat scans using t test and relative risk. Results The number of scans required to complete the anomaly scan was directly related to increasing BMI ( r = 0.243, p < 0.001). 52.1% of obese women required more than one scan to complete the anomaly scan compared to 27.4% of non-obese women (RR 1.90, 95% CI 1.60–2.27, p < 0.001). 12.5% of obese women require more than two scans to complete the anomaly scan compared to 2.35% of non-obese women (RR 5.32, 95% CI 2.97–9.50, p < 0.001). Completion of the initial anomaly scan was not related to gestational age at the time of the scan. Conclusions Obese women required more attempts to complete the anomaly scan and the number of scans required to complete was directly related to booking BMI. There was no relationship between gestation and completion of the scan, suggesting that delaying the anomaly scan to 20 + 6 weeks (or even beyond) would not provide a solution to reducing the requirement for repeat scans. The results provide important information for pre-screening counselling of obese women. Further work is needed to optimize the methods and timing of ultrasound screening to reduce the burden on sonography provision and improve screening outcomes.