Sonar biparietal diameter, femur length, abdominal circumference, femur length/abdominal circumference ratio, ponderal index, and estimated fetal weight were obtained within ten days of delivery of small-for-gestational-age (SGA) (N = 102) and non-SGA (N = 204) newborns. The effectiveness of each ultrasound variable in the antenatal recognition of the SGA fetus was assessed. An abnormal abdominal circumference was the best predictor, confirming SGA in 98% of cases. Other variables (biparietal diameter, femur length, femur length/abdominal circumference ratio, ponderal index, or estimated fetal weight) were less accurate for predicting SGA. When we determined expected results based on a 10% prevalence of SGA, negative predictive value was greater than 92% for all variables studied; however, with the exception of estimated fetal weight and femur length, positive predictive values were disappointing, including abdominal circumference (21%). This report establishes the limits of ultrasound-derived growth variables in the antenatal identification of the SGA fetus.
(C) 1987 The American College of Obstetricians and Gynecologists