The effects of acute uterine ischemia on fetal circulation.

The effects of acute maternal hemorrhage on uterine blood flow and fetal circulation were investigated in pregnant sheep. Nine chronically instrumented pregnant sheep (114-128 d gestation), phlebotomized from the iliac artery at the point of origin of the uterine artery, were studied at baseline, after acute hemorrhage, and immediately and two h after replacement of the blood. Maternal hemorrhage caused a reduction in uterine blood flow as well as both fetal hypoxemia and acidemia. Changes in fetal organ blood flow measured by radionuclide-labeled microspheres showed that blood flow to the brain, heart, and adrenal glands increased (p less than 0.05), whereas blood flow to the other major organs did not change significantly. Rapid replacement of blood restored all parameters to baseline values. We conclude that acute maternal hemorrhage causes a reduction in uterine blood flow, fetal hypoxemia, and acidemia with a secondary increase in blood flow to the high priority organs. Rapid replacement of blood reverses these effects.