CRL discordance in MCDA twin pregnancies as a predictor for late pregnancy complications

Crown-rump length (CRL) is an ultrasonic fetal measurement most commonly used for first trimester GA confirmation. In twin pregnancies, modest size discordancy is a common finding. While most cases are clinically insignificant, CRL discordance above 10% is associated with increased risk for adverse outcome. Such findings could be especially important in MCDA twin pregnancies which carry a particularly high risk for fetal and neonatal complications with a unique subset of potential adverse events. We sought to examine whether discordant CRL measurements, among MCDA pregnancies, could provide a significant predictive value for later pregnancy complications. Study Design: A retrospective cohort study of all MCDA twin pregnancies having their routine prenatal follow-up at a single tertiary center between 2012 and 2019. First trimester sonographic and obstetrical data were retrieved and pregnancies were categorized according to the level of CRL concordance, significant discordance defined as >10%. We then examined rates of late pregnancy complications and adverse outcomes. Results: 74 pregnancies were included in the study, 59 were categorized as concordant and 15 as non-concordant. Although not statistically significant, female fetuses showed higher rates of CRL discordance compared to male fetuses (66.67% vs. 26.67%, p=0.069). We found statistically significant elevated levels of prenatal diagnosis of sFGR for the discordant CRL group (40% vs. 11.86%, p=0.036). However, rates of other prenatal complications attributed to MCDA pregnancies did not seem to differ (TTTS 8.47% vs. 13.33%, p= 0.624, TAPS rates 1.69% vs. 6.67%, p=0.367). GA at delivery averaged lower for the concordant group (32.68 ± 5.47 vs. 35.46 ± 2.32, p=0.005). Conclusion: First trimester CRL discordancy of more than 10% was associated with higher rates of subsequent sFGR diagnosis later during the pregnancy. Further research, with larger cohorts, may provide additional information regarding the role of CRL discordance in predicting other late prenatal complications and adverse outcomes in MCDA pregnancies.