ABSTRACT
These alterations are summarized in Part A
Maternal Cardiovascular System The first two trimesters of pregnancy are generally associated with low blood pressure (BP). In fact, a normal BP during this time may be associated with hypertension. Increased placental blood flow causes arteriovenous shunting of blood, which in turn causes peripheral vasodilation. Other contributors to low BP are increased endothelial synthesis of vascular relaxation factors in the placenta, such as prostaglandins (PGE2 and PGI2), and nitric oxide (NO). The increased cardiac output during pregnancy is a result of cardiac afterload reduction (peripheral vasodilation). Because progesterone increases the ratio of -adrenergic to -adrenergic receptors in myometrial smooth muscle, it may similarly affect vascular smooth muscle, thereby lowering BP.
