Abstract 49

The presence of fetal DNA in maternal plasma and serum was recently recognized, but the underlying process that causes free DNA to be released into maternal circulation has yet to be elucidated. It has been suggested that physical and immunological cell damage and the phenomenon of developmentally regulated apoptosis (Apt) are involved in the process. To clarify this, Apt was determined in the peripheral blood (PB) of 21 pregnant women in the 16th-18th week of pregnancy (16 carrying a normal and 5 an abnormal fetus) before amniocentesis and 20 healthy non-pregnant women. Apt was detected directly in whole peripheral blood suspensions, using the TUNEL assay and was quantitated with the Ethidium Bromide staining method. In non pregnant females Apt was 2.18%±0.32 (range 0.8%-2.3%), while in normal pregnancies it was found to be increased by more than two fold(5.97%±0.50, range 3.7%-8.2%, p<0.0005). In 4 cases where the prenatal diagnosis results showed that the embryo had chromosomal abnormalities, Apt was further increased and was two fold higher than in normal pregnancies (11.8%±1.85, range 9.20%-16.32%), p<0.0005). In one case where the embryo had a 45,XO karyotype Apt in maternal PB was found to be extremely high (34.23%). Fluorescent in situ hybridization in TUNEL positive cells using X and Y specific probes verified the fetal origin of a significant proportion of the apoptotic cell population. These results indicate that during pregnancy the Apt process is stimulated, in the maternal PB, accounting partly for the presence of free fetal DNA in maternal serum. Furthermore, the observation of an increased Apt in pregnancies with abnormal fetuses may have additional clinical importance.