OBJECTIVE The objective of this study was to determine the association of crown-rump length (CRL) discrepancy in monochorionic and dichorionic twins with subsequent pregnancy outcomes. METHODS A retrospective analytical study was performed among 660 twin pregnancies over 12 years in one fetal medicine tertiary referral center in the United Kingdom. A literature search was performed to identify all reports in the English language literature in this topic between 1998 and 2009. RESULTS Five hundred and six dichorionic and 154 monochorionic twin pregnancies were studied. Median percentage CRL discordance in monochorionic and dichorionic pregnancies was not different (3.9 +/- 8.34, range 0-59 and 3.2 +/- 5.65 range 0-37.5, respectively, p = 0.225). Single or double fetal loss was higher in monochorionic twins than the dichorionic twins. Loss rate was 17.53% (27) and 3.95% (20) respectively (p = < .0001). CRL disparity and birth weight discordancy showed statistically significant correlation (Spearman's rho, p = 0.040). Statistically significant correlation was seen between percentage CRL disparity and pregnancy loss rate (p = 0.008). However, the sensitivity of this CRL discrepancy to detect subsequent fetal loss or birth weight discordance is poor. CONCLUSIONS CRL discrepancy is independent of chorionicity in twins. CRL discrepancy is correlated to subsequent pregnancy loss and birth weight discordance, but the clinical utility of this observation is limited. The difference in twin CRL at 11-14 weeks is likely to represent physiological variation in a majority of cases.