68 Dichorionic twin-specific versus singleton growth standards for diagnosis of fetal growth restriction

Abstract

To compare a twin-specific growth standard (NICHD) and a singleton growth curve (Hadlock) in diagnosing fetal growth restriction (FGR) associated with adverse neonatal outcomes in dichorionic diamniotic (DiDi) twin gestations. A retrospective cohort study of DiDi twin gestations ≥32 weeks delivered at a single institution between 2004-2019 with serial growth ultrasounds and neonatal outcomes data. Twins were classified based on last ultrasound before delivery with FGR: by both Hadlock and NICHD, by Hadlock only, and not by either curve, with FGR defined as estimated fetal weight <10%. Multivariate generalized linear mixed models were used to assess adverse neonatal outcomes via pairwise comparisons by FGR group, with a random effects component to account for twin-pair correlations. 1,460 twin infants were included with 8.1% FGR by both NICHD and Hadlock, 8.8% FGR by Hadlock only, and 83.1% with no FGR by either. Compared to twins with no FGR by either curve, twins with FGR by both curves were more likely to experience mild (aOR 2.38; CI 1.38-4.13) and severe (aOR 2.82; CI 1.16-6.88) composite neonatal morbidity. Compared to twins with FGR by Hadlock only, twins with FGR by both curves were more likely to experience mild (aOR 2.03; CI 1.00-4.14), but not severe (aOR 3.70; CI 0.72-18.90), composite neonatal morbidity. No significant differences were found for the studied outcomes between twins with FGR by Hadlock only and twins with no FGR by either curve (Table 1). The NICHD growth standard is a more sensitive marker of FGR that is associated with adverse neonatal outcomes in DiDi twin gestations. Use of Hadlock appears to identify more twins as FGR that are at low risk for neonatal morbidity, which could lead to unnecessary maternal anxiety, increased antenatal testing and possible iatrogenic preterm delivery.