Validity of ultrasound estimation of fetal weight

Objective: To assess the validity of ultrasound estimation of fetal weight at term. Methods: We conducted a prospective observational study whereby all ultraso nic biometric measurements were done by a single observer. Fifty pregnant w omen at term had ultrasonic measurement of various fetal biometric paramete rs performed within a week of delivery. Fetal weight was estimated by the u se of four reported methods (Aoki, Campbell, Shepard, and Hadlock formulas) . We compared estimated weight with the birth weight after the estimated fe tal weight was adjusted by adding 25 g for each day between the ultrasound measurements and delivery. Results: The adjusted estimated fetal weight obtained from all four formula s tended to be lower than measured birth weight. The smallest mean differen ce was obtained with the Shepard and Aoki formulas (51.4 g and 60.5 g, resp ectively), whereas the Campbell and Hadlock formulas produced larger mean d ifferences (141.8 g and 190.7 g, respectively). The Aoki formula generated the smallest range between the limits of agreement (-324.2 to 445.2 g) wher eas the Campbell formula produced the largest range (-286.5 to 570.1 g). Th e range between the limits of agreement generated with the Shepard and Hadl ock formulas were intermediate between those produced by the Aoki and Campb ell formulas. The intraclass correlation coefficients generated with the Ao ki and Shepard formulas were identical (0.90). The intraclass correlation c oefficients obtained with the Hadlock (0.84) and Campbell formulas (0.85) w ere lower. Conclusion: The validity of ultrasonic estimation of fetal weight at term w ith all four formulas was high. (Obstet Gynecol 2000;95:856-60. (C) 2000 by The American College of Obstetricians and Gynecologists).