Effect of labor on uterine blood flow: Observations on gravid ewes

Abstract

Simultaneous direct recordings of maternal blood pressure, intrauterine pressure, and uterine blood flow during ovine labor show that uterine contractions and maternal expulsive efforts decreased uterine blood flow. The acute diminution in blood flow was inversely and quantitatively related to the intensity of uterine contractions and was augmented by superimposed expulsive efforts. Uterine blood flow recovery was dependent upon the duration of the uterine relaxation phase. The present observations in the ewe and reported human observations indicate that uterine blood flow decreases during labor in women and that the average blood flow during a specific interval is determined primarily by the relationship between the intensity and frequency of uterine contractions and the duration of myometrial diastole.