Increased incidence of apoptosis in non-labour-affected cytotrophoblast cells in term fetal membranes overlying the cervix

A regional reduction in the cellularity of the cytotrophoblastic and decidu al layers occurs in the fetal membranes overlying the cervix in the lower u terine segment prior to labour. Although the mechanism(s) involved are not known it could result from regionally increased apoptosis, the histological manifestation of programmed cell death, or decreased proliferation. Apopto sis was assessed in regionally sampled fetal membranes from women undergoin g elective Caesarean section (n = 14) by the presence of apoptotic bodies b y light and electron microscopy. Cell proliferation was assessed by immunoc ytochemical detection of the protein Ki-67. Apoptotic bodies were identifie d in all regions of the fetal membrane with the highest incidence found wit hin the cytotrophoblast layer. However, this layer in fetal membranes biops ied over the cervix contained significantly more apoptotic bodies (mean +/- SD 0.085 +/- 0.020%) compared to the layer in fetal membranes obtained fro m the mid-zone (0.020 +/- 0.008%) apoptotic bodies. Isolated Ki-67 positive cells were detected in the cytotrophoblast layer, but no regional differen ces in their incidence were seen. Fetal membranes also failed to exhibit si gnificant immunoreactivity for BCL-2 but exhibited strong BAX immunoreactiv ity within the decidual layer, We conclude that the regionally increased in cidence of apoptosis in the cytotrophoblastic layer in the membrane overlyi ng the cervix may account for the reduction in its cellularity but not the relative decrease in the decidual layer. Given the consequence, of the loss of local function in degrading uterotonins and stabilizing the fetal membr ane, the study of the regulation of apoptosis in these cells may have impor tant implications for fetal membrane rupture and parturition.