This study aimed to evaluate if an estimated fetal weight (EFW) between 10 and 15th percentiles at the time of anatomy ultrasound, referred to as borderline fetal growth, is associated with progression to fetal growth restriction (FGR) on subsequent ultrasound, delivery of a small for gestational age (SGA) neonate, or neonatal intensive care (NICU) admission.We performed a secondary analysis using the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-be (nuMom2b) data. The exposures were normotensive pregnancies with non-anomalous singleton gestations with normal growth, defined as EFW >
15th percentile at the anatomy scan compared to borderline fetal growth fetuses defined as those with an EFW in the 10 to 15th percentiles. The primary outcome was FGR at subsequent ultrasound, defined as EFW or AC <
10%. The secondary outcomes were NICU admission and SGA neonate. Univariable analyses were performed comparing maternal baseline demographic and clinical characteristics. Multivariable analysis was performed for the primary outcome with variables adjusted a priori for body mass index, smoking status, race/ethnicity, insurance status, and drug use.In total, 4,883 patients met inclusion criteria with 114 in the borderline fetal growth group and 4,769 in the normal growth group. There were no significant differences in maternal demographic or medical characteristics. In adjusted multivariable analysis, patients with borderline growth had significantly higher odds of being diagnosed with FGR at their subsequent scan (adjusted odds ratio [aOR] = 6.68, confidence interval [CI]: 3.98-11.20) compared to those with normal growth. For secondary outcomes, patients with borderline fetal growth were significantly more likely to have SGA neonates (6.14 vs. 2.67%,