Clinical implications of first trimester crown-rump length discordance in dichorionic twin gestations

Abstract

First trimester crown-rump length (CRL) discordance (≥10% difference in CRL) in monochorionic twins is associated with adverse perinatal outcomes (APO). However, data are limited on clinical implications of CRL discordance in dichorionic (DC) twins. We therefore aimed to evaluate if first trimester CRL discordance in DC twins is associated with APOs or aneuploidy in either twin. This is a secondary analysis of data from a multicenter retrospective cohort study, evaluating cfDNA performance for common trisomies in patients with twin pregnancies from 12/2011-02/2020. We included live DC pregnancies with CRL measurements between 11-14 weeks gestation. The primary composite APO outcome was defined as any 1 of the following: preterm birth or severe preeclampsia < 34 weeks, birthweight discordance ≥ 20%, birthweight < 10%ile of either twin, or stillbirth >20 weeks in one or both twins. The secondary outcome was the rate of composite aneuploidy (T21, T18, T13) in either twin. Outcomes between twin pairs were compared via chi-squared and t-test as appropriate. Multivariable logistic regression was used to calculate odds ratios and adjust for confounders. Of the 1,110 DC twin gestations meeting inclusion criteria, 156 (14.1%) had discordant CRLs. There were no differences in demographics between twins with and without CRL discordance (Table 1). The mean maternal age for the cohort was 35 and 33% were nulliparous. The rate of APO was higher with discordant CRLs after adjusting for aneuploidy (73.1% vs 60.0%, aOR 1.73, 95% CI 1.18-2.53), driven mostly by birthweight outcomes (Table 2). The overall rate of aneuploidy was 3.9% and twins with discordant CRLs had more than 3-fold increased odds of aneuploidy (9.6% vs 3.2%, OR 3.16, 95% CI 1.66-6.01). CRL discordance in DC twin pregnancies is associated with increased risk for adverse perinatal outcomes and aneuploidy. This data may prove useful in decisions about aneuploidy screening or diagnostic testing, and in the identification of DC pregnancies that require increased surveillance.View Large Image Figure ViewerDownload Hi-res image Download (PPT)