The association of gestational age discrepancy in the growth restricted fetus at anatomy ultrasound with small for gestational age neonates: a retrospective cohort study.

To evaluate the association between gestational age (GA) discrepancy in FGR fetuses at time of anatomy US with small for gestational age neonates, as well as evaluate the risk of persistent FGR and adverse perinatal outcomes. Retrospective cohort study of pregnant patients with singleton, non-anomalous gestations diagnosed with FGR at anatomy US performed between 18w0d-21w6d from January 2021 to December 2023. Patients were grouped by GA discrepancy: >10 days vs ≤10 days from EDD. Our primary outcome was SGA neonate at delivery and secondary outcomes included persistent FGR at subsequent ultrasound and adverse perinatal outcomes. Univariable analysis evaluated baseline maternal demographic and clinical differences. Multivariable regression adjusted for a priori maternal age and race/ethnicity. 68 patients met inclusion criteria with 13 (19%) with measured GA > 10 days and 55 (81%) with FGR with measured GA ≤ 10 days. GA > 10 days had a lower weight percentile at anatomy US compared to GA ≤ 10 days (1% vs 7%, p < .001) and lower birthweight (2400 g vs. 2680 g, p = .030). GA > 10 days had more SGA neonates (53.9% vs 45.5%) but these findings were not significant (RR 1.40, 95% CI 0.416, 4.708) and persisted in multivariable analysis, (aRR 1.48, 95% CI 0.428, 5.091). GA > 10 days were more likely to have persistent FGR and 5-min Apgar score <3. There were no differences in other maternal and perinatal outcomes. A GA discrepancy >10 days in FGR at anatomy scan was not associated with an increased risk of SGA but was associated with an increased risk of persistent FGR and 5-min Apgar scores <3.