Abstract： Objective To investigate the intrauterine growth characteristics of twins and birthweight discordant twins (discordant twins ).Methods Total of 1010 twin pregnancies (2020 fetuses) with complete delivery records from the Department of Obstetrics and Gynecology,the First and Third Affiliated Hospital of SUN Yat-sen University between January 1,2000 and July 31,2010 were studied retrospectively.One handred and ninteen cases (238 fetuses) with intrapair birthweight difference ≥25％ were determined as the discordant twins group,and the other 891 cases (1782 fetuses) with intrapair birthweight difference ＜ 25％ were identified as the concordant twins group.The singleton control group included 4042 singleton pregnancies in the same period.Results ( 1 ) Comparison of clinical data between the twins groups:the birthweight of larger-twin,smaller-twin and intrapair birthweight difference in the discordant twins group and the concordant twins group were ( 2090± 827 ) g,( 1392 ± 592 ) g,( 33.9 ±9.3 ) ％,and ( 2408 ± 543 ) g,( 2191 ± 505 ) g,( 8.9 ± 6.5 ) ％,respectively,with significant differences (P＜0.01).The incidence of discordant twins was 11.78％ (119/1010).Compared with the concordant twins group,the discordant twins group bad higher proportion of monochorionic twins,and higher prevalence of pregnancy complications such as late miscarriage,abnormal umbilical insertion,twin-twin transfusion syndrome and hypertensive disorders in pregnancy ( P ＜ 0.05 ).( 2 ) The characteristics of twin birthweight distribution:① In all the 2020 twins,80.05％ (1617/2020) fetuses had birthweight below the 50th percentile of the singleton control group,while 23.71％ (479/2020) feeuses got birthweight below the 10th percentile of the singleton control group.② After 19th gestational week,the 50th and 90th percentile of all twins' birthweight were lower than those of singletons.After 38th gestational week,the birthweight of singletons kept increasing and reached its peak at 41 th week,while the birthweight of twins reached its peak at 38th week,followed by a decline at 39 weeks,which was even lower than the 10th percentile of the singleton control group.③ The distribution of birthweight of larger- and smaller-twin in the discordant twins group:65 (54.6％,65/119) larger-twins and one (0.8％,1/119) smaller-twin had birthweight above the 50th percentile of all twins,while 5 (4.2％,5/119) larger-twins and 97 ( 81.5％,97/119 ) smaller-twins got birthweight below the 10th percentile of all twins.Conclusions ( 1 ) The patterns of birthweight curves for each gestational week are different between twins and singletons.In order to evaluate the growth of twins, birthweight reference for twins shoull be employed.( 2 ) According to the reference of twins birthweight,the most discordant twins are complicated with fetal growth restriction at least in one twin.