REGRESSION FORMULA FOR ESTIMATION OF FETAL WEIGHT WITH USE OF ABDOMINAL CIRCUMFERENCE AND FEMUR LENGTH - A PROSPECTIVE-STUDY

Ultrasonographic fetal measurements from 293 singleton pregnancies were obtained within 7 days of delivery. Biparietal diameter, abdominal circumference, femur length, and actual birth weight data of the first 93 fetuses in the study were used as variables to determine the best mathematical model for relating estimated fetal weight to biparietal diameter, abdominal circumference, and femur length. With the aid of a computer, three regression equations were derived. The best model was Log10 (weight) = 0.77125 + 0.13244 (AC) - 0.12996 (FL) - 1.73588 (AC x AC)/1000 + 3.09212 (FL x AC)/1000 + 2.18984 (FL/AC); (R2 = 0.987). The accuracy of this formula was then compared prospectively, first with the formulas published by Shepard and coworkers, Rose and McCallum, and Hadlock and colleagues in the entire sample of 200 patients, second in 46 large, 101 appropriate, and 53 small for gestational age fetuses, and then in 44 fetuses of pregnancy complicated by diabetes. The difference between actual and estimated birth weights generated by the study formula had no systematic error (Student's t-test, P > 0.05) in cumulative data, and in small or appropriate and large for gestational age fetuses. As this derived formula is very cumbersome to manipulate, tables have been prepared with computer assistance to read the estimated fetal weight directly.