Comparison of three sonographic circumference measurement techniques to predict birth weight

Objective: To compare the accuracy of three different sonographic circumfer ence measurement techniques in predicting birth weight in term fetuses, usi ng 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 dia meter (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, el lipse, and trace). With the use of each circumference method, estimated fet al weights were determined for each fetus according to a weight-estimation formula incorporating BPD, HC, AC, and FL. The accuracy of the formula usin g each circumference measurement technique for predicting actual birth weig ht was calculated. Results: The mean (a standard deviation [SD]) gestational age was 38.1 +/- 0.9 weeks and the mean actual birth weight was 3536 +/- 472 g, The two-diam eter and ellipse circumference measurements allowed more accurate birth wei ght prediction than did the trace method, with mean (a SD) percent deviatio ns 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, wi th 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 ell ipse method yielded predicted birth weights within 10% of actual birth weig hts in 77.4 and 79.2% of cases, respectively. Conclusion: Two-diameter and ellipse circumference measurement techniques a re similarly accurate in predicting birth weight and both are significantly better than the trace technique. (C) 1999 by The American College of Obste tricians and Gynecologists.