Objective To conduct prenatal diagnosis of positive 21-trisomy syndrome results by DNA noninvasive prenatal testing . Methods Amniocentesis , cordocentesis and fluorescence in situ hybridization ( FISH ) were used to analyze fetal karyotype .High-throughput DNA technique was applied to detect placenta , and the causes of DNA noninvasive prenatal testing of false positive results were analyzed.Results The result of amniocentesis was 46, XN/47, XN, +21(141/5), shown as 21-trisomy mosaicism karyotype.The FISH results and cordocentesis were normal .Placental location and maternal fetal surface were normal karyotype with 21-trisomy mosaicism karyotype , while fetal placenta and umbilical cord tissue surface were normal karyotype , which was known as confined placental mosaicism (CPM).Conclusion There are false positive results in DNA noninvasive prenatal testing .DNA noninvasive positive results have to be determined by amniocentesis and (or) cordocentesis.Amniocentesis suspected mosaicism needs to be diagnosed by cordocentesis .%目的：对无创DNA检查21-三体综合征阳性的胎儿进行产前诊断。方法采用羊膜腔穿刺术及脐血穿刺术，通过细胞培养方法及荧光原位杂交技术（ FISH）对胎儿细胞进行染色体核型分析。运用高通量DNA技术对胎盘进行检测，分析无创DNA检查假阳性结果的原因。结果羊水细胞核型分析结果为46，XN/47，XN，＋21（141/5），为21-三体嵌合体核型。羊水细胞FISH结果正常。脐血穿刺胎儿染色体正常。胎盘中心位置及母胎面为正常核型和21-三体嵌合体核型，胎盘胎儿面及脐带组织为正常核型，为限制性胎盘嵌合体。结论无创DNA检查存在假阳性结果。无创DNA检查阳性结果必须通过羊膜腔穿刺和（或）脐血穿刺进行确诊。羊水染色体疑似嵌合现象必须通过脐血穿刺进行确诊。
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