An evaluation of two equations for predicting fetal weight by ultrasound.

In an earlier study we presented a method of determining fetal weight from ultrasound measurements of abdominal circumference (AC) and biparietal diameter (BPD). From an equation with these two measurements as independent variables we generated tables of estimated fetal weights (E1). Although these tables have been very useful, we had the impression we were underestimating fetal weight. Therefore, we reconsidered an earlier unpublished table generated from a different equation (E2). While most estimates from E1 and E2 were likely to be within 10% of actual weight, there was significant underestimation with E1. E2 provides a better balance between the distribution of overestimations and underestimations.