By using a simple model, transformed to cartesian coordinates, we examined the behavior of the fetal and maternal oxygen partial pressure on the terminal villus of the human placenta during a constant arteriovenous oxygen difference. For this purpose we divided the flow length of the cotyledon in central and a peripheral part. We found that the oxygen exchange takes place at a lower utero-umbilical oxygen pressure gradient it the reduction of the maternal blood flow velocity amounts to 30% of the normal value and if the diffusion distance is doubled. However under these circumstances a sufficient the oxygen supply of the fetal organism. This is the case with the total flow length of a single cotyledon, but some of the terminal villi in the periphery of the cotyledon, could receive at the same time a diminished oxygen supply leading to degenerative cell changes. At a progression of these morphological changes or during labor the oxygen transport can get insufficient.