Ultrasonic fetal weight estimation: analysis of inter- and intra-observer variability.

Standard ultrasound measurements were performed by two observers in 40 third-trimester fetuses. Observers were blinded to the results of the measurements. Estimated fetal weight (EFW) was calculated using two published formulae. The intra-observer standard deviation for EFW, assessed using one-way analysis of variance, was < 75 g for both observers. The 95% prediction intervals for inter-observer comparisons of EFW, calculated using the limits of agreement method, were -187.3 g to 139.8 g, and -159.9 g to 124.3 g, using the two formulae. The results suggest that measurements of EFW are reproducible. The prediction interval is comparable to the weekly fetal weight increment in normal fetuses.