Does an Early Isolated Decrease in Fetal Abdominal Circumference Heighten the Risk of Growth Restriction? [ID 1300]

INTRODUCTION: This study investigated if an isolated second-trimester fetal abdominal circumference (AC) less than 10th percentile (ACL10) is a risk factor for fetal growth restriction (FGR) and small for gestational age (SGA) neonates. 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 ACL10, measured between 18 and 24 weeks of gestation. Control participants were randomly selected from the same time period. Congenital anomalies were excluded. RESULTS: A total of 589 out of 1,213 patients met inclusion criteria (ACL10 n=213; control n=376). Mean AC was 6.3 percentile in ACL10 and 51.2 percentile in controls. Birth weight (2,782 g versus 3,257 g, P <.001) and percentiles (18.3% versus 41.8%, P <.001) were lower in ACL10. Abdominal circumference was an independent risk factor for FGR (adjusted odds ratio [aOR] 12.5 [6.7, 23.4]) and SGA (aOR 5.08 [3.32, 7.76]). Although more pregestational diabetic mothers were ACL10 (10.3% versus 3.7%, P =.001), pregestational diabetes was protective of FGR (aOR 0.15 [0.04, 0.54]). As maternal body mass index (BMI) increased, likelihood of FGR (aOR 0.95 [0.90, 0.995]) and SGA (aOR 0.94 [0.91, 0.97]) decreased. Black patients were more likely to have ACL10 (36.2% versus 25.8%, P =.027). There were no differences in parity, gestational diabetes, chronic/gestational hypertension, preeclampsia, BMI, or mode of delivery between cohorts. CONCLUSIONS/IMPLICATIONS: Isolated second-trimester ACL10 in an otherwise normally grown fetus is an independent risk factor for both FGR and SGA. Increased maternal BMI was protective of FGR and SGA. Pregestational diabetes was protective of FGR but not SGA.