Adverse birth outcomes in relation to prenatal sonographic measurements of fetal size

Objective. To evaluate and quantify the prediction of multiple neonatal outcomes by sonographically estimated fetal weight across a broad range of gestational ages. Methods. A retrospective cohort analysis was conducted among women with certain gestational age (n = 1376) seen at the University of California San Francisco from 1994 through 1997. The relative risks for small size at birth, small (low birth weight) for gestational age, and adverse neonatal outcomes were compared between small and average-sized fetuses. Results. Fetuses with an estimated fetal weight in the 5th percentile or less for gestational age were at increased risk of a birth weight less than 2000 g (relative risk, 6.5), a birth weight in less than the 3rd percentile for gestational age (relative risk, 10.1), preterm birth (relative risk, 2.2), extreme preterm birth (relative risk, 5.7), prolonged neonatal hospital stay (relative risk, 2.7), neonatal intensive care unit admission (relative risk, 3.2), and stillbirth or neonatal death (relative risk, 7.7) compared with average-sized fetuses (all P <.0001). With intrauterine growth restriction defined as an estimated fetal weight in the 5th percentile or less for gestational age, up to 29% of fetuses with adverse neonatal outcomes were detected, for false-positive rates of only 4% to 5%. After adjusting for confounding variables, low estimated fetal weight remained a significant predictor of neonatal morbidity and mortality. Conclusions. Morbidity and mortality are significantly increased among fetuses with an estimated fetal weight in the 5th percentile or less for gestational age.