Fibrinolytic activity is depressed during pregnancy and labor, although the precise mechanism is unkown. The placenta may be partially responsible for this alteration in fibrinolytic status. Plasminogen levels increase concomitantly with fibrinogens levels, causing an equilibrationof clotting and lysing activity. Clearly, coagolation and fibrinolytic sistems undergo major alterations during pregnancy. As the uterus enlarges and the diaphragm becomes elevated, the heart is displaced upward and somewhat to the left with rotation on its long axis, so that the apex beat is moved laterally.
Cardiac output is very sensitive to changes in body position.
This sesitivity increases with leghthening gestation, presumably because the uterus impinges upon the inferior vena cava, thereby decreasing blood return to the heart. Blood Pressure Systemic blood pressure declines slightly during pregnancy. Diastolic pressure increases thereafter to prepregnancy levels by about 36 weeks. The obstruction posed by the uterus on the inferior vena cava and the pressure of fetal presentig part on the commom illiac vein can result in decreased blood return to the heart. This decreases cardiac output, leads to a fall in blood pressure, and causes edema in the lower extremities.