Impact of Using Abdominal Circumference Independently in the Diagnosis of Fetal Growth Restriction

Objective: Society for Maternal-Fetal Medicine guidelines for diagnosing fetal growth restriction (FGR) have broadened the definition to include abdominal circumference (AC) <10^th percentile for gestational age (GA) regardless of estimated fetal weight (EFW). We aimed to compare the ability of three definitions of FGR to predict small for gestational age (SGA) neonates and adverse outcomes. Methods: We performed a secondary analysis of a prospective cohort of patients who underwent assessment of fetal growth between GA of 26 and 36 weeks. We compared three definitions of FGR: EFW <10^th percentile; AC <10^th percentile; either EFW or AC <10^th percentile. The primary outcome was successful prediction of neonatal SGA. Secondary outcomes included a composite adverse neonatal outcome (CANO). We further compared these definitions of FGR using area under receiver operative curves (AUC) to measure their discriminatory abilities. Results: About 1054 women met inclusion criteria. Ninety-one (8.6%) had EFW <10^th percentile, 122 (11.6%) had AC <10^th percentile, and 137 (12.9%) had either EFW or AC <10^th percentile. SGA was seen in 139 (13.2%); CANO was seen in 139 (13.2%). Ability for detecting neonatal SGA was significantly better when the definition included both EFW or AC <10^th percentile compared to either variable independently. The AUC were: 0.74, 0.73, 0.69; P =.0003. There was no statistical significance in ability for predicting CANO (AUC 0.51, 0.51, 0.50; P =.7447). Conclusions: Addition of AC as a criterion for diagnosing FGR improves our ability to predict neonatal SGA compared to using EFW alone. All three definitions were poorly predictive of neonates at risk for adverse outcomes.