Final answer:
During pregnancy, maternal blood volume significantly increases, leading to hemodilution where the blood is diluted, causing decreased concentration of red blood cells. This physiological change accommodates the growing needs of the fetus and adjusts maternal circulation and blood pressure.
Step-by-step explanation:
During pregnancy, the maternal blood volume increases substantially, so that by childbirth, it may exceed its pre-pregnancy volume by approximately 30 percent, or about 1-2 liters. This increase in blood volume is crucial for efficiently meeting the increased demands of fetal nourishment and waste removal. The increase in volume can cause hemodilution, a condition where the blood becomes diluted due to the additional plasma volume, leading to a decrease in the concentration of red blood cells and other blood components.
As a consequence of hemodilution, pregnant individuals may experience a physiological anemia, which is a normal change during pregnancy, because, while there is an increase in red cell mass, it is not proportional to the increase in plasma volume. This adaptative mechanism ensures adequate blood flow to the uterine and placental circulation and accommodates the requirements of the growing fetus and maternal tissues.
Moreover, as pregnancy progresses, various circulatory changes occur such as a moderate rise in pulse and blood pressure and the compression of pelvic blood vessels by the enlarging uterus, which can lead to an increased risk of varicose veins or hemorrhoids due to impaired venous return.