Abstract: ObjectiveTo investigate the correlative factors of low birthweight in twin pregnancies.MethodsThe sample consisted of 657 livebirth pairs of twins was grouped into three categories:both-twins with low-birthweight,one-twin with low-birthweight and both-twins with normal birthweight.To analyze the relation of low birthweight with gender and birth order within pairs.To compare the maternal factors among the 3 group including age of maters,gestational age,gravida,parity,blood pressure and hemoglobin(Hb).ResultsThere were more low-bithweight fetuses in 2nd twins,or in female ones.The maternal gestational age and parity were significantly different among the 3 groups.In the low-birthweight groups,the diastolic blood pressure was lower than that of the normal group in early pregnant period,and the maternal Hb was higher all the time.ConclusionThe gender,birth order,gestation age,and parity are the correlative factors of low birthweight in twins.At pregnant period,the relation for maternal Hb and diastolic blood pressure with low birthweight of twins may be a "maternal adaptation" to twin pregnancy,but need more research.