1.3 Physiological aspects

1.3.1 Physiology of pregnancy

Functional and structural alterations develop in the entire body during the course of pregnancy and delivery. Early changes are due, in part, to the energy 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 changes, starting in mid-pregnancy, are anatomical in nature and are caused by mechanical pressure from the expanding uterus.

Cardio-vascular system of the mother

The pregnancy-induced changes in the cardio-vascular system develop primarily to meet the increased metabolic demands of the mother and fetus. Despite the increased workload of the heart during gestation and labour, the healthy woman has no impairment of cardiac reserve.

Blood Volume increases progressively from 6-8 weeks of gestation and reaches a maximum at approximately 32-34 weeks with very little change thereafter. The increase in plasma volume (40-50%) is relatively greater than that of red cell mass (20-30%) resulting in decrease in hemoglobin levels. Hence, intake of supplemental iron and folic acid is necessary to restore hemoglobin levels to normal (12 g/ dl).

Blood Pressure is never increased during normal pregnancy. In fact, by mid-pregnancy, a slight decrease in diastolic pressure can be recognized. Increase of blood pressure in response to stress is more pronounced during pregnancy.