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目的:对单绒毛膜双羊膜囊（monochorionic diamniotic, MCDA）双胎染色体核型不一致进行遗传学分析。方法:回顾性分析2016年1月至2019年12月在广西壮族自治区妇幼保健院超声诊断为MCDA双胎并经产前诊断为染色体核型不一致的4例孕妇。所有孕妇均在超声定位下行双羊膜腔穿刺，分别取双胎羊水同时进行染色体核型分析和单核苷酸多态性（single nucleotide polymorphism, SNP）芯片检测，并根据SNP基因型分析确定合子性质。结果:4例MCDA双胎染色体核型不一致，分别为47,XX,+18和46,XX、45,X和46,XX、47,XXY[17]/46,XY[33]和47,XXY、47,XX,+21和46,XX；SNP芯片结果分别为arr(18)×3和arr(1-22,X)×2、arr(X)×1和arr(1-22,X)×2、arr(X)×1~2,(Y)×1和arr(X)×2,(Y)×1、arr(21)×3和arr(21)×2~3。SNP基因型分析证实4例MCDA双胎均为单合子双胎。4例中，3例因胎儿染色体异常选择引产，1例失访。1例再次妊娠生育1子，现体健。结论:临床工作中应警惕MCDA双胎染色体核型不一致情况发生。未来可以积累MCDA双胎染色体核型不一致相关病例并进一步探讨其遗传学机制。“,”Objective:To explore the genetic background in monochorionic diamniotic (MCDA) twins discordant for karyotypes.Methods:This study retrospectively analyzed four pregnant women who were diagnosed as having MCDA twins with prenatal diagnostic indications by ultrasound at Maternity and Child Health Care of Guangxi Zhuang Autonomous Region from January 2016 to December 2019. Dual amniocentesis was performed for all cases guided by ultrasound and the twin amniotic fluids were taken for karyotyping and single nucleotide polymorphism (SNP) array testing. Zygosity was determined by SNP genotype analysis.Results:The karyotypes of four MCDA twins were 47,XX,+18 and 46,XX, 45,X and 46,XX, 47,XXY[17]/46,XY[33] and 47,XXY, and 47,XX,+21 and 46,XX, respectively. The results of SNP were arr(18)×3 and arr(1-22,X)×2, arr(X)×1 and arr(1-22,X)×2, arr(X)×1~2,(Y)×1 and arr(X)×2,(Y)×1, arr(21)×3 and arr(21)×2~3. All of them were monozygotic twins according to the SNP genotypes. Three out of the four cases chose to terminate the pregnancy due to fetal chromosomal abnormalities and one was lost to follow-up. One gave birth to a healthy child in the next pregnancy.Conclusions:Clinicians should be alert to the discordant karyotypes in MCDA twins, of which the mechanism is yet to be explored.