Comparison of ultrasound accuracy versus clinical fetal weight estimation - a retrospective cross-sectional study

Estimating fetal weight (EFW) is essential for decisions regarding mode of delivery, labour induction, and identification of at-risk fetuses. Deviations from expected weight may lead to labour complications and maternal or neonatal injury; therefore, abnormalities must be detected before delivery. There are two most used methods of EFW: ultrasound (US) biometry, requiring highly skilled staff and equipment, and widely available clinical examination (O/E) based on measurements of the dimensions of a mother. To compare the accuracy of two EFW methods: US examination performed according to ISUOG guidelines, with Hadlock IV (BPD-HC-AC-FL) formula vs O/E performed by midwives in a real-life clinical setting.

The study was conducted using the dataset from electronic patient records (2742 records) of gestational-age patients between 37 and 42 weeks who gave birth between January 2017 and July 2020 in St. Sophia's Hospital in Warsaw. Both methods' accuracy was judged by comparing the variations between the EFW in both forms and the actual birth weight (ABW) for each patient.

Results measured using US, and O/E, compared to ABW varied significantly (p < 0.001). The study revealed that, on average, ultrasound tended to underestimate fetal weight, whereas O/E frequently overestimated it. The discrepancy in EFW using these methods was most pronounced at the extreme ends of fetal weight measurements. Additionally, factors such as fetal age, fetal length, and gestational age significantly influenced the accuracy of these measurements, as evidenced by multivariate regression analysis.

Clinical examination can complement ultrasound in fetal weight estimation, but further studies are needed to improve EFW accuracy and support safer obstetric decision-making.