(457) Association between definitions of fetal growth restriction and placental insufficiency

Contemporary definitions of fetal growth restriction (FGR) include diagnosis by AC< 10^th percentile alone, with controversy if similar perinatal risk exists in this cohort of patients.  We aimed to examine the prevalence of placental pathology, a marker of placental insufficiency, in association with classic vs contemporary definition of FGR.

Study Design:

This is a retrospective study of patients in a large health system from 01/2021 to 01/2025 diagnosed with FGR on ultrasound within 1 month of delivery. The exposure of FGR was classified based on the contemporary (AC < 10^th percentile and EFW > 10^th percentile) vs traditional (EFW < 10^th percentile with or without AC < 10^th percentile) definitions. Our primary outcome was placental insufficiency, determined by presence of maternal vascular malperfusion (MVM) by a single perinatal pathologist. Secondary outcomes included fetal vascular malformation (FVM), chronic inflammation (CI), and acute inflammation (AI), and a composite of chronic pathology (MVM, FVM, CI). Statistical analyses included chi-square, Wilcoxon rank-sum, T-test for univariate analysis and logistic regression for multivariable analysis, adjusted for age, BMI, race and gestational diabetes.

Results:

400 patients had FGR and placental pathology available during the study period, 146 patients with traditional and 254 patients with contemporary definition. There were no demographic differences (Table 1). Across both diagnostic definitions, there was a high prevalence of placental insufficiency. There was no difference in the presence of MVM between the two groups (98 (67.1%) traditional vs 166 (65.4%) contemporary, p=0.72, aOR 1.04 95% CI 0.67-1.62, Table 2). The majority of patients in both cohorts had chronic placental pathology (88.4% traditional vs 88.2% contemporary, p=0.96, aOR 1.05 95% CI 0.55-2.01, Table 2).

Conclusion:

FGR diagnosed by contemporary and traditional definitions have similarly high rates of placental insufficiency, supporting equal management of patients given the known association of placental insufficiency and adverse perinatal outcomes including stillbirth.