Background The role of first trimester ultrasound in predicting the outcome in twin pregnancies is conflicting. The aim of this study is to determine the association between crown-rump length (CRL) discordance and adverse perinatal outcome in twin pregnancies.

Methodology CRL discordance was related to early fetal loss <20, <24 weeks, perinatal mortality, birth weight (BW) and ultrasound estimated fetal weight (USS EFW) discordance ≥25%, intrauterine growth restriction (IUGR) and preterm birth <34 weeks of gestation. ROC and logistic regression analysis was performed to evaluate the importance CRL discordance in determining adverse perinatal outcome.

Results A total of 2,155 twin pregnancies [420 monochorionic (MC) and 1,735 dichorionic (DC)] were included in the study. CRL discordance had very poor prediction for fetal loss <20 (AUC of 0.61), < 24 weeks (AUC: 0.54), perinatal mortality (AUC of 0.52), BW discordance (AUC of 0.61), BW < 5th centile (AUC of 0.56), USS EFW discordance (AUC of 0.55) and preterm birth (AUC of 0.50). Overall mortality was significantly higher (p = 0.016) in MC (21/420) compared to DC (45/1735) twins. Logistic regression analysis demonstrated that chorionicity (p = 0.033 OR: 2.09, 95% C.I. from 1.06 to 4.010) independently contribute in determining mortality while CRL discordance (p = 0.201) did not. After adjusting for chorionicity, CRL discrepancy did not improve the detection of adverse outcome in either MC or DC twin pregnancies.

Conclusion CRL discordance is of poor predictive value for adverse perinatal outcomeafter 14 weeks of gestation in either MC or DC twin pregnancies.