Accuracy of Ultrasound Estimation of Fetal Weight at Term: A Comparison of Shepard and Hadlock Methods

BACKGROUND: Ultrasound measurement provides a noninvasive means of obtaining information about fetal weight and may help in necessary preparations at and after delivery. Although some ultrasound methods include only one or two fetal indices, others, to improve accuracy, incorporate either three or all the four fetal indices. The aim of this report is to assess the accuracy of two different methods for fetal weight estimation. MATERIALS AND METHODS: This was a prospective study of 170 consecutive pregnant women at term. Ultrasound was used to estimate fetal weight by the Shepard and Hadlock methods, and the actual birth weight (ABW) was determined at birth. The ultrasound-estimated fetal weights (EFWs) and ABW were analyzed. RESULTS: The women were aged 21–42 years (mean 31.3 ± 7 years). The EFW using the Shepard method was 1.9 kg–5.0 kg (mean 3.6 ± 0.5 kg) and 1.8 kg–4.4 kg (mean 3.3 ± 0.4 kg) for Hadlock method, and ABW was 2.0 kg–4.5 kg (mean 3.4 ± 0.5 kg). The mean EFW using the Shepard method was significantly higher than that of ABW (P < 0.001). The Shepard method significantly overestimated macrosomia compared to that by the ABW. There was no significant difference in microsomia rate between the two methods and ABW. CONCLUSION: The Hadlock method was more accurate at estimating fetal weight compared to the Shepard method and is recommended for the ultrasound estimation of fetal weight in our setting and similar settings.