Incidence of neonatal morbidity in small‐for‐gestational‐age twins based on singleton and twin charts

Abstract

ObjectiveUsing lengths of stay in neonatal intensive care unit (NICU) as a measure of morbidity, the objective is to compare twins and singletons according to classification of small for gestational age (SGA) using the 10th percentile for twins or the 10th percentile for singletons.MethodsNICU lengths of stay were compared in 1,150 twins neonates and 29,035 singleton neonates all scanned at between 35+0 and 36+6 weeks’ gestation. Estimated fetal weights were obtained from measurements of head circumference, abdominal circumference and femur length using the Hadlock formula. Gestational ages were obtained from first trimester crown rump length measurements using the larger of the two twins. Singletons and twins were compared for NICU lengths of stay according to classification as small relative to the Fetal Medicine Foundation singleton and twin reference distributions.ResultsThe overall proportions of neonates entering NICU for twins and singletons were similar (7.3% vs, 7.4%), but twins tended to have longer lengths of stay in NICU (≥7 days: 2.4% of twins vs. 0.8% of singletons, relative risk 3.0, 95% CI: 1.6 – 4.4). Using singleton charts, a much higher proportion of twins were classified as SGA than singletons (37.2% vs. 7.0%). However, the proportion of SGA neonates entering NICU was similar (10.3% for twins and 10.1% for singletons) and the proportions of SGA neonates spending ≥7 days in NICU was substantially higher for twins than for singletons (3.7% vs. 1.4%, risk ratio 2.6, 95% CI: 1.1 – 4.7).ConclusionsWhen singleton charts are used to define SGA in twins and in singletons, there is a greater degree of growth‐related neonatal morbidity amongst SGA twins than in SGA singletons. Consequently, use of singleton charts in twins does not inappropriately over diagnose fetal growth restriction and they should be used for monitoring fetal growth both in twins and in singletons.This article is protected by copyright. All rights reserved.