Placental blood flows and oxygen transfer during uterine contractions: A mathematical model

Theoretical calculations have been performed on the effects of changes in intrauterine pressure on maternal and fetal placental blood flows and pressures and transplacental O₂ exchange. Initial conditions and contraction profiles may be “assumed normal” or abnormal. The model predicts that the fetal O₂ deficit is most sensitive to the maximum intensity of the contraction and maternal mean arterial blood pressure, less sensitive to the duration of the contraction and far less sensitive to the value of maternal arterial PO₂. The umbilical venous PO₂ falls to a minimum at the peak of a contraction. Its level is most sensitive to contraction intensity and maternal blood pressure; while the value of maternal arterial PO₂ has less effect and the duration of contraction has essentially no effect. There is interaction between factors so that the effect of simultaneous changes is not necessarily in proportion to the effects of individual changes.