Apoptosis in fetal nucleated erythrocytes circulating in maternal blood

The purpose of this study was to determine if apoptosis occurs in fetal cells that have crossed into the maternal circulation, which would potentially explain the difference between the number of intact fetal cells and the amount of fetal DNA detectable in maternal plasma. We flow-sorted fetal nucleated erythrocytes (FNRBCs) using antibody to the gamma chain of fetal haemoglobin and confirmed them to be fetal in origin by FISH analysis using chromosome-specific probes. Fetal cells were then analysed microscopically for the presence of terminal UdTP nuclear end labelling (TUNEL) staining. Apoptotic change was observed in 42.7% of fetal NRBCs (106/246) and 3.5% of maternal cells (29/818). Results of this study indicate that a significant number of fetal cells in maternal blood are undergoing apoptosis at the time of sampling. Apoptosis may be one mechanism by which fetal cells are cleared by the maternal circulation.