(1151) Does an Early Isolated Increase in Fetal Abdominal Circumference Heighten the Risk of Macrosomia?

Objective: To determine if an isolated second trimester fetal abdominal circumference (AC) >90th %tile is an independent risk factor for large for gestational age (LGA) neonates and macrosomia.

Study Design: This multi-center retrospective cohort study analyzed patients who delivered term singletons between 1/1/2019-1/1/2024. The exposed group involved normally grown fetuses with isolated AC’s >90th %tile, measured between 18 and 24 weeks gestation. Control subjects were matched in a 1:1 ratio from the same period. Congenital anomalies were excluded. Statistical analyses included independent t-tests for continuous variables, chi-squared tests for categorical variables, and binary logistic regression models for LGA and macrosomia.

Results: Of the 1,188 patients screened, 752 met inclusion criteria (n=376 per cohort). Mean AC in the AC >90 group was 94%tile compared to 51%tile in controls. Birthweights were higher in the AC >90 group (3,629g vs. 3,257g, p< 0.001). Rates of LGA (29.5% vs. 6.6%, p< 0.001) and macrosomia (15.2% vs. 2.9%, p< 0.001) were higher in the AC >90 group. AC >90%tile was an independent risk factor for both LGA (AOR 7.05 [3.43, 14.52]) and macrosomia (AOR 4.51 [2.78, 7.32]). Additional logistic regressions are shown in Table 1. Higher maternal BMI increased the risk of LGA and macrosomia. There were no differences in parity, pregestational or gestational diabetes, or mode of delivery between cohorts. Gestational hypertension was more prevalent in the AC >90 group (13.8% vs. 9.0%, p=0.039), whereas chronic hypertension was more prevalent among controls (13.3% vs. 7.2%, p=0.006). A sub-analysis of macrosomic infants is shown in Table 2. Macrosomic infants in the AC >90 group trended toward higher rates of lacerations (72.7% vs. 33.3%) and shoulder dystocia (9.1% vs. 0%), although overall incidence was low.

Conclusion: An isolated second trimester AC >90th %tile in an otherwise normally grown fetus is an independent risk factor for both LGA and macrosomia. An isolated increase in AC may also be a risk factor for lacerations and shoulder dystocia at birth, but further research is required.