A primipara patient who takes prenatal vitamins daily asks the nurse the etiology of her physiological anemia. The nurse replies that in physiological anemia of pregnancy, lower hemoglobin and hematocrit is due to

increased plasma volume


• To provide an adequate exchange of nutrients in the placenta and to compensate for blood loss at birth, the circulatory blood volume of the woman’s body increases at least 30% during pregnancy. Although red cell mass also increases, plasma volume increases more, causing hemodilution and a lower hemoglobin and hematocrit.

• The increase in blood volume occurs gradually near the end of the first trimester. It peaks at about the 28th to the 32nd week and continues at this high level through the third trimester. 

• Iron absorption may be impaired during pregnancy as a result of decreased gastric acidity, and additional iron is often prescribed during pregnancy to prevent true anemia, but physiologic anemia is seen in most women simply due to hemodilution.

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