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Uterine blood flow has been measured with a chronically implanted miniature electromegnetic flow meter in unanesthetized pregnant sheep and dogs during spontaneous and oxytocin induced labor and followed in the same animal for several postpartum days. In either spontaneous or oxytocin induced labor, uterine contractions are accompanied by a significant decrease in uterine blood flow and relaxations by the return of the flow to or higher than control values. The decrease is roughly proportional to the intensity of uterine contraction. When the contraction is of a tetanic nature and not followed by relaxation, uterine ischemia is so severe that the fetus might succumb. After the delivery of the fetus and before the expulsion of the placenta, uterine blood flow falls slightly. However, after separation and expulsion of the placenta, uterine blood flow falls precipitously. Thereafter, a very slight and progressive decrease continues for several days paralleling uterine involution.
Assali et al. (Sun,) studied this question.