ESTIMATORS OF BIRTH-WEIGHT IN PREGNANT-WOMEN REQUIRING INSULIN - A COMPARISON OF 7 SONOGRAPHIC MODELS

Objective: To determine if the relative accuracy of the sonographic es timate of birth weight among diabetic gravidas requiring insulin impro ves significantly as more fetal measurements are used. Methods: We stu died 172 diabetic women requiring insulin who had sonographic measurem ents of fetal parts within 7 days of delivery. Friedman nonparametric analysis of variance followed by Dunn multiple comparison and X(2) wer e used to assess the relative accuracy of the seven models. Prediction limits were calculated to determine the estimate of fetal weight that would ensure (with 90% accuracy) that the newborn was macrosomic (at least 4 kg). Results: The mean (+/- standard deviation [SD]) birth wei ght was 3388 +/- 727 g, and the frequency of macrosomia at term gestat ion was 19.4% (29 of 149). The mean standardized absolute error (g/kg) based on abdominal circumference (AC) and femur length (FL) (86 +/- 7 2 g/kg) was not significantly different from the other models (range 8 4 +/- 72 to 116 +/- 99 g/kg, P > .05). The percent of estimate within 10% of actual birth weight using AC and FL (65%) was similar to the ot her models (53.4-66.2%). Regardless of the White classification, the e stimation of fetal weight using AC and FL had an accuracy similar to t he other six regression equations. To ensure that the birth weight is at most 3999 g, the estimated fetal weight should be 3200 g, and, conv ersely, if the predicted weight is 4700 g, then the newborn is macroso mic. Conclusion: Among patients requiring insulin, estimation of birth weight using AC and FL is as accurate as more complicated models. The ability to detect macrosomia by ultrasound is limited.