Circulation in the Pregnant Uterus

The primary blood supply to the uterus is the uterine artery, a major branch of the hypogastric or internal iliac artery. In the fetus this same hypogastric artery gives rise to the umbilical artery, which delivers nearly 50% of the cardiac output to the placenta. This fact is mentioned in order to stress the remarkable capability of this particular portion of the vascular system to accommodate a tremendous increase in blood flow during pregnancy. The uterine arteries descend for a short distance (about 4 cm) after dividing from the hypogastric (internal iliac) artery. In the base of the broad ligament, the uterine artery progresses medially, crossing anterior to the ureter about 2 cm lateral to its division into the cervicovaginal artery and the ascending uterine artery at the level of the supravaginal portion of the cervix. The ascending branch runs a tortuous course along the lateral margin of the uterus, providing a major branch to the upper portion of the cervix and eight to 24 arcuate branches to the uterus1 (Fig. 1). The tortuosity of the uterine artery as it traverses the broad ligament and as it ascends the uterus is directly related to the woman′s parity. The arteries of parous women assume a much more convoluted and tortuous course.