Physiological and anatomical alterations develop in many organ systems during the course of pregnancy and delivery. Early changes are due, in part, to the metabolic demands brought on by the fetus, placenta and uterus and, in part, to the increasing levels of pregnancy hormones, particularly those of progesterone and oestrogen. Later anatomical changes, starting in mid-pregnancy, are caused by mechanical pressure from the expanding uterus.
The pregnancy-induced changes in the cardiovascular system develop primarily to meet the increased metabolic demands of the mother and fetus. The increased metabolic demand of the mother occurs particularly in organs such as the kidneys, breasts and uterus.
Blood volume, increases progressively from 7 weeks and reaches a maximum at 33 weeks. Most of the added volume of blood is accounted for by an increased capacity of the uterine, breast, renal, muscle and adipose tissues.
Increases to a similar degree as the blood volume. Steady rises are due to an increase in stroke volume and also to a more rapid heart rate.