Does an Early Isolated Increase in Fetal Abdominal Circumference Heighten the Risk of Macrosomia? [ID 1242]

INTRODUCTION: This study investigated if isolated second-trimester fetal abdominal circumference (AC) greater than 90th percentile (ACG90) is a risk factor for large for gestational age (LGA) and macrosomia. METHODS: This multicenter retrospective cohort study analyzed patients who delivered term singletons between January 1, 2019, and January 1, 2024. The exposed group involved otherwise normally grown fetuses with isolated ACG90, measured between 18 and 24 weeks of gestation. Control participants were matched in a 1:1 ratio from the same period. Congenital anomalies were excluded. RESULTS: A total of 752 out of 1,188 patients met inclusion criteria (n=376 per cohort). Mean AC was 94th percentile in ACG90 and 51st percentile in controls. Birth weights were higher with ACG90 (3,629 g versus 3,257 g, P <.001). Rates of LGA (29.5% versus 6.6%, P <.001) and macrosomia (15.2% versus 2.9%, P <.001) were higher with ACG90. ACG90 was an independent risk factor for LGA (adjusted odds ratio [aOR] 7.05 [3.43, 14.52]) and macrosomia (aOR 4.51 [2.78, 7.32]). Higher maternal body mass index increased risks of LGA/macrosomia. There were no differences in parity, pregestational/gestational diabetes, or mode of delivery between cohorts. Gestational hypertension was more prevalent with ACG90 (13.8% versus 9.0%, P =.039), whereas chronic hypertension was more frequent among controls (13.3% versus 7.2%, P =.006). Subanalysis of macrosomic infants revealed ACG90 trended toward more frequent lacerations (72.7% versus 33.3%) and shoulder dystocia (9.1% versus 0%), although overall incidence was low. CONCLUSIONS/IMPLICATIONS: Isolated second-trimester ACG90 in an otherwise normally grown fetus is an independent risk factor for LGA/macrosomia. Isolated increased AC may be a risk factor for lacerations and shoulder dystocia.