Rapid clearance of fetal DNA from maternal plasma

Fetal DNA has been detected in maternal plasma during pregnancy. We investi gated the clearance of circulating fetal DNA after delivery, using quantita tive PCR analysis of the sex-determining region Y gene as a marker for male fetuses. We analyzed plasma samples from 12 women 1-42 d after delivery of male babies and found that circulating fetal DNA was undetectable by day 1 after delivery. To obtain a higher time-resolution picture of fetal DNA cl earance, we performed serial sampling of eight women, which indicated that most women (seven) had undetectable levels of circulating fetal DNA by 2 h postpartum. The mean half-life for circulating fetal DNA was 16.3 min (rang e 4-30 min). Plasma nucleases were found to account for only part of the cl earance of plasma fetal DNA, The rapid turnover of circulating DNA suggests that plasma DNA analysis may be less susceptible to false-positive results , which result from carryover from previous pregnancies, than is the detect ion of fetal cells in maternal blood; also, rapid turnover may be useful fo r the monitoring of fete-maternal events with rapid dynamics. These results also may have implications for the study of other types of nonhost DNA in plasma, such as circulating tumor-derived and graft-derived DNA in oncology and transplant patients, respectively.