Effects of symmetric and asymmetric fetal growth on pregnancy outcomes

Objective: To assess the prevalence of head circumference to abdomen circum ference (HC/AC) asymmetry among small for gestational age (SGA) fetuses, an d to determine the likelihood of adverse outcomes among asymmetric and symm etric SGA infants compared with their appropriate for gestational age (AGA) counterparts. Methods: In a retrospective cohort study, we analyzed consecutive live-born singletons of women who had antepartum sonography within 4 weeks of delive ry and delivered between January 1, 1989 and September 30, 1996. A gestatio nal age-specific HC/AC nomogram was derived from our sonographic database o f 33,740 nonanomalous live-born singletons. Asymmetric HC/AC was defined as greater than or equal to the 95th percentile for gestational age. Results: Among 1364 SGA infants, 20% had asymmetric HC/AC and 80% were symm etric. Asymmetric SGA infants were more likely to have major anomalies than symmetric SGA infants or AGA infants (14% versus 4% versus 3%, respectivel y; P < .001). After exclusion of anomalous infants, pregnancy-induced hyper tension at or before 32 weeks' gestation and cesarean delivery for nonreass uring fetal heart rate were more common in the asymmetric SGA than the AGA group (7% versus 1% and 15% versus 3%, respectively; both P < .001). A neon atal outcome composite, including one or more of respiratory distress, intr aventricular hemorrhage, sepsis, or neonatal death, was more frequent among asymmetric SGA than AGA infants (14% versus 5%, P = .001). Symmetric SGA i nfants were not at increased risk of morbidity compared with AGA infants. Conclusion: The minority of SGA fetuses with HC/AC asymmetry are at increas ed risk for intrapartum and neonatal complications. (Obstet Gynecol 2000;96 :321-7. (C) 2000 by The American College of Obstetricians and Gynecologists ).