Diabetic macrosomia: accuracy of third trimester ultrasound.

Sonar biparietal diameter, head circumference, and abdominal circumference percentile values obtained late in the third trimester were compared with birth weight percentile (relative to dates) in 147 diabetic mothers and 40 control fetuses of nondiabetics. Estimates of fetal weight by the method of Shepard et al were also calculated from these sonar data and compared with birth weight percentile. Abdominal circumference values greater than the 90th percentile correctly predicted macrosomia (defined as birth weight greater than 90th percentile) in 78% of cases. Biparietal diameter and head circumference percentiles were significantly less predictive of macrosomia. When analyzed in a similar manner, estimated fetal weights greater than the 90th percentile correctly predicted macrosomia at birth in 74% of cases. However, when both the abdominal circumference and the estimated fetal weight exceeded the 90th percentile, macrosomia was correctly diagnosed in 88.8% of pregnant women with diabetes mellitus.