Predictive Values of Sonographic Parameters for Antenatal Diagnosis of Small for Gestational Age Fetus

Abstract

This prospective study examined the reliability of various sonographic parameters in detecting SGA fetus in utero. Sonographic BPD, AC, HC/AC ratio, FL/AC ratio, EFW and AFV were obtained within ten days of delivery of SGA (N=221) and non-SGA (N=276) newborns. The effectiveness of each ultrasound variable for antenatal diagnosis of the SGA fetus was assessed. Predictive values were computed using Bayes theorem and based upon a 10% prevalence rate of SGA. An HC/AC ratio was the best predictor, which could detect 87% of SGA with 76% of positive predictive value. Other variables (AC, FL/AC, EFW, AFV, BPD) were less accurate for predicting SGA. Negative predictive value was greater than 92% for all variables. However, with the exception for HC/AC and FL/AC ratios, the positive predictive values were disappointing. This report establishes the limi tations of each ultrasound parameter in the antenatal diagnosis of the SGA fetus. (Thai J Obstet Gynaecol 1993;5:7-14.)