Abstract: ObjectiveTo evaluate prenatal diagnosis value of chromosomal karyo types for fetus of mid-orlate pregnary.MethodsChromosomal karyo types of cells in amniotic fluid or cord blood were analyzed among 2 948 fetuses in 16.36 weeks of pregnancy with signs for prenatal diagnosis.ResultsTotally 272 cases of abnormal chromosomal karyo-types were identified among the pregnancies with a positive rates of 9.3%.The rate of abnormal autosomal and sex chromo some were 98.8% and 1.2%,respectively.Polymorph ismand number abnormality were the most common among the auto-somal and sex chromosome.ConclusionThe most frequent abnormal chromo somal are chromo somal polymorphismand number abnormality for fetuses with signs for pregnatal diagnosis.Prenatal diagnosis with chromo somal karyo types analysis is helpful in reducing new born with abnormal chromo somal karyo types.