OC22.02: Crown–rump length discordance in first trimester; a predictor of adverse outcome in dichorionic pregnancies?

To evaluate the usefulness of first trimester crown–rump length (CRL) discordance in predicting adverse outcome in dichorionic twin pregnancies. This retrospective study included a large cohort retrieved from local ultrasound databases at 14 obstetric departments in Denmark, comprising all dichorionic twin pregnancies with two live fetuses scanned between 11 and 14 weeks' gestation in the period 1 January 2004 to 31 December 2006. Gestational age was based on CRL of the largest twin at the 11–14 week scan. The association between a CRL discordance ≥10 % and adverse outcome was evaluated. Among 1733 dichorionic twin pregnancies, 156 (9%) were discordant and 1577 (91%) were concordant. We found a significant association between CRL discordance ≥10 % and fetal loss/preterm delivery before 34 weeks (p=0.001), preterm delivery before 34 weeks (p=0.007), birth weight discordance (p=0.001) and mean birth weight (p=0.033). To evaluate CRL discordance as a predictor of fetal loss/preterm delivery before 34 weeks, and birth weight discordance ≥20%, receiver operating characteristics (ROC) curves were created for each outcome. For CRL discordance as a predictor of fetal loss/preterm delivery before 34 weeks sensitivity was 0.51 (95% CI 0.45-0.57), specificity 0.63 (95% CI 0.59-0.64). For CRL discordance as predictor of birth weight discordance ≥20%, sensitivity and specificity was 0.30 (95% CI 0.24-0.35) and 0.82 (95% CI 0.81-0.85), respectively. Using CRL discordance ≥ 10%, sensitivity was 0.14 (95% CI 0.10-0.18) and specificity 0.92 (95% CI 0.91-0.94), in terms of the outcome fetal loss/preterm delivery before 34 weeks. CRL discordance in dichorionic twin pregnancies is associated with, but is not a strong predictor of, adverse outcome.