Time Profile of Appearance and Disappearance of Circulating Placenta-Derived mRNA in Maternal Plasma

Fetal RNA of placental origin has been detected in the plasma of pregnant women, but the timing of the first appearance and the detailed kinetics of postdelivery clearance of such circulating RNA have not been studied. To address the timing of the first appearance of circulating placental RNA, we collected serial maternal blood samples from 47 women who had conceived by assisted reproductive procedures. To address the postdelivery clearance kinetics, we collected serial postdelivery blood samples from 6 pregnant women who had delivered by cesarean section. Placenta-derived transcripts were sought by real-time quantitative reverse transcription-PCR. The earliest gestational age at which human placental lactogen and human chorionic gonadotropin beta-subunit mRNAs were detectable in a proportion of the pregnant women was the 4th week of gestation. The postdelivery study indicated that the median apparent half-life for the clearance of human placental lactogen mRNA was 14 min. Placenta-derived mRNA can be found in maternal plasma from very early on in gestation, suggesting a possible role for early noninvasive prenatal diagnosis or monitoring. The rapid kinetics of circulating placental mRNA suggest that its plasma concentrations may be used to monitor recent physiologic or pathologic events.