Comparison of three sonographic circumference measurement techniques to predict birth weight*1

Abstract

Objective: To compare the accuracy of three different sonographic circumference measurement techniques in predicting birth weight in term fetuses, using a standard equation for estimating fetal weight. Methods: Fifty-three singleton, term fetuses were examined sonographically within 24 hours of scheduled elective cesarean delivery. The biparietal diameter (BPD) and femur length (FL) were measured using standard techniques, and head circumference (HC) and abdominal circumference (AC) were measured using three separate circumference measurement techniques (Two-diameter, ellipse, and trace). With the use of each circumference method, estimated fetal weights were determined for each fetus according to a weight-estimation formula incorporating BPD, HC, AC, and FL. The accuracy of the formula using each circumference measurement technique for predicting actual birth weight was calculated. Results: The mean (± standard deviation [SD]) gestational age was 38.1 ± 0.9 weeks and the mean actual birth weight was 3536 ± 472 g. The two-diameter and ellipse circumference measurements allowed more accurate birth weight prediction than did the trace method, with mean (± SD) percent deviations from the actual birth weight of –0.5 ± 7.8%, 1.9 ± 8.0%, and 8.2 ± 11.6% (P < .05), respectively. The trace method was the least accurate, with a mean birth weight overestimation of 266 g and measurements within 10% of the actual birth weight only 49.1% of the time. The two-diameter and ellipse method yielded predicted birth weights within 10% of actual birth weights in 77.4 and 79.2% of cases, respectively. Conclusion: Two-diameter and ellipse circumference measurement techniques are similarly accurate in predicting birth weight and both are significantly better than the trace technique.