Influence of maternal body mass index on ultrasound estimation of fetal weight

Background: Obesity is one of the most common public health problems. According to ACOG committee opinion, at least one-third of the pregnant women are obese. With the increasing prevalence in the general reproductive-age population, the prevalence of obesity in pregnancy has also increased markedly.Obesity in pregnancy is associated with multiple obstetrical complications. Many important clinical decisions depend on accurate determination of Estimated fetal weight. Despite considerable technical advances in ultrasound technology, ultrasound imaging of obese patients remains challenging due to the adverse effects of adipose tissue on the propagation of sound waves. Obesity impairs the visualization of fetal anatomy and degrades the image quality making it difficult for interpretation of fetal weight. Aim: To study the possible effect of maternal obesity on the fetal weight estimated sonographically in the third trimester, maximum of 7 days before labour. Objectives: To study the possible effect of maternal obesity on the fetal weight estimated sonographically in the third trimester, maximum of 7 days before labour.To compare the accuracy of this estimation among normal weight, overweight, and class I, class II and class III obese women. Methods: This is a retrospective study of 100 singleton pregnancies with sonographic fetal weight estimation prior to scheduled delivery. Women were classified into five categories based on BMI (according to WHO guidelines): normal weight, BMI 18.5-24.9 kg/m2 (n=20); overweight, BMI 25.0-29.9 kg/m2 (n=20); obese class I, BMI 30.0-34.9 kg/m2 (n=20); obese class II, BMI 35.0-39.9kg/m2 (n=20); and obese class III, BMI ? 40.0 kg/m2 (n=20). The fetal weight estimated sonographically was compared with actual birth weight and the difference between them was recorded as the error. Results: Fetal weight estimation error rose markedly with BMI: MAE increased from 105.75±67.58 g (normal) to ~380 g in obese class II-III, and MAPE increased from 3.69±2.38% to ~12%, with both MAE and MAPE differing significantly across BMI categories (p< 0.001), indicating substantially reduced accuracy of fetal weight estimation in higher BMI strata Conclusion: Increasing subcutaneous tissue and altered acoustic windows in obesity can reduce image quality and compromise the precision of fetal biometry, potentially leading to under-measurement of parameters incorporated into EFW formulas. This study emphasises the need for heightened caution when interpreting EFW in higher BMI. The present study has shown that increasing maternal obesity decreases the accuracy of sonographic EFW measurement.