Objective To investigate the distribution of fetal discrepancy in twins during the first trimester,and its influencing factor.Methods This was a prospective analysis of twin pregnancies that underwent 11 +0-13 +6 week scan at a tertiary hospital from Sep 2008 to May 2012.Differences in crownrump length (CRL),nuchal translucency (NT) were calculated for each twin pair and their distribution was analyzed according to chorionicity,gestational age,mode of conception,and the gender.Results A total of 86 twin pregnancies were included,20(23.3％) were monochorionic and 66 (76.7％) were dichorionic twins.The average discrepancy in CRLs and NTs was (3.03 ± 2.70) mm and (0.27 ± 0.20) mm respectively.There was no significant different in the CRL and NT discrepancy between monochorionic and dichorionic twin pairs.The overall CRL and NT discrepancy were not change significantly with gestational age,mode of reception or gender.Conclusions Discrepancy of CRL,NT from 11+0 to 13+6 weeks of gestation are not significantly correlated with chorionicity,gestational age,mode of conception and fetal gender.