Fetal Medicine Foundation charts for fetal growth in twins

To derive reference distributions of estimated fetal weight (EFW) in twins relative to singletons.Gestational age and chorionicity-specific reference distributions for singleton percentiles and EFW were fitted to data on 4,391 twin pregnancies with two liveborn fetuses from four European centres; there were 3,323 dichorionic (DC) and 1,068 monochorionic diamniotic (MCDA) twin pregnancies. Gestational age was derived using the larger of the two crown-rump length measurements obtained during the first trimester of pregnancy. The EFW was obtained from ultrasound measurements of head circumference, abdominal circumference, and femur length using the Hadlock formula. Singleton percentiles were obtained using the Fetal Medicine Foundation population weight charts for singleton percentiles. Hierarchical models were fitted to singleton z-scores with autoregressive terms for serial correlations within and between twins; separate models were fitted to DC and MCDA twins.Fetuses from twin pregnancies tended to be smaller than singletons at the earliest gestations; 16 weeks for MCDA and 20 weeks for DC twins. This was followed by a period of catch-up growth to around 24 weeks. After that, both DC and MCDA twins showed reduced growth. In DC twins, the EFW corresponding to the 50th percentile was on the 50th percentile of singleton pregnancies at 24 weeks, the 43rd percentile at 28 weeks, the 31st percentile at 32 weeks, and the 22nd percentile at 36 weeks. In MCDA twins, the EFW corresponding to the 50th percentile was on the 36th percentile of singleton pregnancies at 24 weeks, the 29th at 28 weeks, the 19th at 32 weeks, and the 12th at 36 weeks.In DC and, to a greater extent, MCDA twin pregnancies, fetal growth demonstrates a comparatively lower rate than that observed in singleton pregnancies. Furthermore, the divergence in growth trajectories between twin and singleton pregnancies becomes more pronounced as gestational age increases. This article is protected by copyright. All rights reserved.