['The present study was designed to give possible answers to some of the discrepancies regarding the presence or not of intact fetal cells in maternal plasma during pregnancy.', '12-mL peripheral blood was collected from 33 pregnant women in the second trimester: 6 mL was harvested by 3-step Percoll gradient centrifugation and plasma cells were analyzed by FISH with X/Y chromosome specific probes. From the remaining 6 mL, plasma-derived cells were isolated with three different gradient centrifugation protocols and apoptosis was determined following EthBr staining.', 'The number of cells recovered ranged from 900 to 3000. At least one Y positive signal was seen in 12 out of 17 cases with male fetuses at a frequency of 0.12% (range 0.05-0.27%). No XY cells were detected in the plasma of women carrying female fetuses. Hybridization efficiency was <60%. EthBr staining demonstrated that the majority of these cells were in their late apoptosis.'] Are fetal cells in maternal plasma found in a late state of apoptosis?