Factors Influencing the Accuracy of Sonography-estimated Fetal Weight: A Retrospective Cohort Study in the Chinese Population

Abstract

Objective: To evaluate the accuracy of sonography-estimated fetal weight (EFW) and to determine the potential factors influencing EFW accuracy in the Chinese population. Methods: Eleven widely used formulae were chosen to evaluate the accuracy of EFW in 7016 cases in a retrospective cohort study. Nine potential factors (prenatal body mass index [BMI], gestational age [GA], birth weight [BW], fetal sex, fetal presentation, amniotic fluid volume [AFV], seniority of sonographers, the time interval between ultrasonic measurement and delivery, and diabetes mellitus) were analyzed by binary logistic regression to determine whether they influenced sonography-EFW. Results: All 11 models had high correlation coefficients between EFW and BW (r = 0.819–0.843). Model 3 was the most accurate formula for the Chinese population. Compared to fetuses with EFW of 2500–3999 g, the accuracy of EFW decreased by 69.10% (P <0.001) for fetuses less than 2500 g, and decreased by 54.10% (P <0.001) for fetuses larger than 4000 g. The accuracy of EFW in female fetuses decreased by 12.70% compared with male fetuses (P = 0.021). Compared to the EFW calculated 1-3 days before delivery, the accuracy of the EFW performed 4–7 days before delivery showed a significant decrease (P = 0.014). The accuracy of EFW was influenced by the individual measurement accuracy of the sonographers. Maternal BMI, DM, GA, fetal presentation, and AFV did not influence the accuracy of EFW after adjustment. Conclusion: Model 3 was the most accurate model for the Chinese population. The BW, fetal sex, time interval, and technique of the sonographers had different influences on the accuracy of EFW.