Ultrasonic estimation of fetal weight

To generate formulas to estimate fetal weight on the basis of sonographic measurements, 226 pregnant women were scanned within 3 days of delivery. Measurements included: biparietal diameter, head circumference and area, abdominal circumference and area, and femoral length. The contribution of each parameter to the estimation of fetal weight was tested by stepwise regression analysis. The best dependent variable was found to be the log of weight. The formula based on cranial and abdominal parameters proved to be inaccurate, especially when fetal weight was less than 2500 g. The addition of femoral length improved weight estimation, with a multiple r of 0.95174. The addition of gestational age led to even more accurate formulas. The most accurate found was based on biparietal diameter, abdominal circumference, femoral length and gestational age, with a multiple r of 0.95651 and an absolute mean error of 7.976 +/- 5.657%. It also produced better weight estimates at the 2 extremes of fetal weight.