Modifications of the maternal organism during pregnancy.

Pregnancy induces numerous changes in the physiology of the woman. Those ch anges are necessary for the embryo and fetus to have a normal growth, and f or the woman to adapt to that physiologic event A 50% raised cardiac flow is the consequence of increased systolic flow and cardiac frequency. Blood volume is about 40 % larger than in non-pregnant woman. It is the consequence of enlargement of the plasmatic volume (50 %), and the red cells mass (30 %). Those different changes explain the physiol ogic anemia of pregnancy. The main part of the blood volume increase corres ponds to an enlargement of the venous system, but without any change of the central venous pressure. Arterial pressure remains unchanged throught the pregnancy, or sometimes gently decreases (10 %). Those changes are more imp ortant during an effort, particularly during the labor Increase of cerebral blood flow (as a consequence of a raised cardiac flow) is limited by the cerebral autoregulation. As a consequence. there is no e vidence for dramatic cerebral hemodynamic changes during pregnancy. Neverth eless, autoregulation is less effective for arterial pressure over than 150 mmNg, what can induce an hemorrhagic stroke. Blood levels of steroid (progesterone, oestrogens) and peptidic (HCG, NPL) hormones are increased. Oestrogens are said to make capillary fragile, and progesterone is responsible for the enlargement of the venous system. In order to prevent an hemorrhagic accident, pregnancy induces a lack of fi brinolysis, and an Excess in coagulation. The consequence is the ability of the pregnant and post-partum woman to develop venous thrombosis.