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目的 本文旨在分析确定妊娠早、中、晚各期母血中胎儿DNA的含量,从而为利用孕母血浆循环DNA进行病理性妊娠诊断研究奠定基础.方法 收集746例不同孕期孕妇抗凝血,通过实时荧光定量聚合酶链式反应(FQ-PCR)技术测定高甲基化RASSF1A基因含量,确定不同孕期孕周孕妇外周血浆中胎儿DNA含量.结果 孕妇早、中、晚期孕组血浆胎儿DNA平均含量分别34.68土24.76copies/μL、204.03±124.91copies/μL、338.84土345.15 copies/μL,三组比较有显著性差异(P＜0.05).孕妇血浆中的高甲基化RASSF1A水平随着孕周的增长而增高.最早可在7周检测到孕妇血浆中高甲基化RASSF1A基因,含量随妊娠的进程逐渐增加,且在分娩后三天内消失.10例健康未妊娠女性血浆均未检出高甲基化RASSF1A基因.结论 用实时荧光定量PCR的方法可确定正常孕妇血浆中不同孕期孕周胎儿DNA的含量,为后续病理性妊娠诊断研究提供实验依据.“,”Objective:To determine the content of fetal RASSF1A gene in maternal plasma of early,middle and late pregnancy women respectively.Methods:746 cases of pregnant women plasma in different pregnancy phases were collected.Plasma DNA was extracted,then digested with methylation-sensitive restriction enzyme (BstUI) and the fetal specific DNA (cffDNA) concentration in different stage of pregnancy was quantified by real-time polymerase chain reaction (FQ-PCR).Plasma cffDNA levels were compared in three different pregnancy stage groups.Results:The mean concentration of hyperrmethylated RASSF1A gene in the early,middle and late pregnancy groups were 34.68±24.76copies/μL、204.03±124.91copies/μL、338.84±345.15copies/μL,with significant difference among the three groups (P＜0.05).Conclusion:The fetal specific epigenetic marker in maternal plasma was demonstrated in a large study group of normal pregnant women.Findings would form the basis of future studies involving pregnancy complications that would aid in the early diagnosis of placental pathologies with hypermethylated RASSF1A gene.