Hemodynamic changes during pregnancy in the rabbit.

Blood volume (BV), plasma volume (PV), red cell volume (RCV), cardiac output (CO), and organ blood flows were measured in nonpregnant (Group I), 10 to 19 days' pregnant (Group II), and 20 to 30 days' pregnant (Group III) rabbits. BV, PV, and RCV increased throughout pregnancy, with maximum increase during the second third of gestation. CO peaked during the second third of gestation and then decreased. Mean arterial pressure and systemic vascular resistance decreased. Total reproductive blood flow increased throughout pregnancy but when calculated per unit of weight it did not change. Redistribution of blood flow within the reproductive organs occurred, with ovarian and placental flow per unit of weight increasing and myometrial flow/unit of weight decreasing. Splenic flow decreased significantly; liver flow decreased. The flow to the lungs and kidneys remained unchanged. The data suggested that major hemodynamic changes occur during the first two thirds of gestation and this period appears to test the competency of the maternal organism to adapt to the needs of pregnancy. The last one third of gestation is characterized by the fetoplacental unit interaction.