Physiology of the prenatal oxygen supply
The prenatal oxygen supply gets optimized by three factors:
All three factors are important for an efficient gas exchange and play a role in the different compartments of the maternal and infant blood. In the following diagram the O2 binding curves of the maternal and fetal blood at the time of birth are shown for the mean pH value in the placenta. In order to take into account the various hemoglobin concentrations of mother and fetus (12g/% and 18g/%, respectively), not the O2 saturation is displayed on the ordinate but rather the O2 concentration.
The O2 concentrations as a function of the O2 partial pressure (PO2) for the maternal and fetal blood at the time of birth are shown on the two lines. During the gas exchange process in the placenta the O2 concentration in the maternal blood sinks around 9 volume %, while that of the fetal blood increases around 7 vol.%.
Please note that, for the same partial pressure (e.g. 50 mm Hg), fetal blood can bind considerably more O2 (22%) than that of the mother (12%).