Effects of symmetric and asymmetric fetal growth on pregnancy outcomes.

OBJECTIVE: To assess the prevalence of head circumference to abdomen circumference (HC/AC) asymmetry among small for gestational age (SGA) fetuses, and to determine the likelihood of adverse outcomes among asymmetric and symmetric 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 delivery and delivered between January 1, 1989 and September 30, 1996. A gestational age-specific HC/AC nomogram was derived from our sonographic database of 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 symmetric. Asymmetric SGA infants were more likely to have major anomalies than symmetric SGA infants or AGA infants (14% versus 4% versus 3%, respectively; P <.001). After exclusion of anomalous infants, pregnancy-induced hypertension at or before 32 weeks' gestation and cesarean delivery for nonreassuring 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 neonatal outcome composite, including one or more of respiratory distress, intraventricular hemorrhage, sepsis, or neonatal death, was more frequent among asymmetric SGA than AGA infants (14% versus 5%, P =.001). Symmetric SGA infants were not at increased risk of morbidity compared with AGA infants.

CONCLUSION: The minority of SGA fetuses with HC/AC asymmetry are at increased risk for intrapartum and neonatal complications.