Comparing outcomes of fetal growth restriction defined by estimated fetal weight versus isolated abdominal circumference

Purpose: The objective of this study was to compare maternal and neonatal outcomes when the diagnosis of FGR was based on isolated abdominal circumference < 10th percentile for gestational age (GA) (iAC group) versus overall estimated fetal weight < 10th percentile (EFW group).Methods: This was a retrospective cohort study of singleton gestations who underwent growth ultrasounds and delivered at a single health system from 1/1/19-9/4/20. The study group was comprised of patients with AC < 10th percentile and EFW >= than the 10th percentile (iAC group). The control group included patients with overall EFW < 10th percentile (EFW group). Outcomes evaluated included GA at delivery, mode of delivery, fetal and neonatal outcomes. Data was analyzed using Mann Whitney U, X-2, and Fisher exact tests with significance defined as p < 0.05.Results: 635 women met the inclusion criteria, 259 women in the iAC group and 376 women in the EFW group. The iAC group was noted to have a later GA at diagnosis and delivery. iAC was associated with lower rates of preterm birth (PTB), NICU admission, SGA at delivery and umbilical artery cord gas < 7.0.Conclusion: Using iAC as a definition of FGR increased the number of FGR cases by 1.69-fold over EFW criteria alone. However, obstetrical and neonatal outcomes for the iAC group appear to be significantly better than those in the EFW group, with low rates of PTB, NICU admission, and umbilical artery cord gas < 7.0.