Uterine blood flow: periodic fluctuations of its rate during pregnancy

Daily measurements of the rate of uterine blood flow (ml/min) during the last half of pregnancy of four normal sheep reflected a 17-day cyclic fluctuation (range, 9.5-42 days) superimposed on a linear increase over time. The cyclic increase was not detected in two (of 7) intact ewes or in four pregnant ewes that had been ovariectomized. The cyclic pattern of increase may be related to ovarian activity.