Intrapartum fetal weight estimation: a comparison of three formulae

To determine the relative accuracy of fetal weight estimation using the biparietal diameter (BPD), the abdominal circumference (AC), and the femur length (FL) in three formulae (BPD/AC, FL/AC, and BPD/AC/FL), 63 patients in labor were examined. All patients delivered within 24 hours of ultrasound examination. A good correlation was found between the estimated fetal weight and the actual birth weight, using the three formulae: BPD/AC (r = 0.96); FL/AC (r = 0.95); and BPD/AC/FL (r = 0.96). The FL/AC formula overestimated fetal weight (P less than 0.01), however, particularly in fetuses weighing more than 2000 g. The mean percentage error with the BPD/AC formula was 0.99 per cent, 3.82 per cent with the FL/AC, and 2.43 per cent with the BPD/AC/FL formula. This study showed that although all three formulae were comparable, the best estimation of the birth weight was obtained when either the BPD/AC or the BPD/AC/FL formulae were used. Additionally, the results demonstrate that reliable estimates of fetal weight can be made even at term or in laboring patients.