Routine Ultrasound Screening for Early Detection of Small for Gestational Age Fetuses

Abstract

A real-time ultrasound screening examination was performed in 3208 unselected singleton pregnancies at 18 and 34 weeks to detect small for gestational age (SGA) fetuses below the tenth percentile weight for age. Such cases accounted for 4.9% of this population. Biparietal diameter (6PD) was used at the first examination to confirm the true gestational age. The growth was measured at 34 weeks with a combination of BPD and transverse abdominal diameter. With a cutoff level of -1.5 standard deviations (SD), the sensitivity of a single measurement was 62.2%, the specificity was 93.2%, and the positive predictive value was 32.4%. With a cutoff level of - 1 SD, the values were 76.3, 84.8, and 20.4%, respectively. The positive predictive value approached 48.7% before birth in the group that was rescanned before delivery. The simple method of a combined measurement of BPD and transverse abdominal diameter provided efficient antenatal screening for diagnosis of SGA fetuses in the general population. A somewhat low positive predictive value indicates a control examination of fetuses suspected of being SGA. Nonlinear methods, such as the measurement of abdominal circumference, appear suitable for ruling out false-positive cases.