What causes physiologic anemia in pregnancy?

Physiologic anemia in pregnancy primarily results from an increase in plasma volume, which can rise by as much as 50% by the end of the second trimester. This substantial increase in plasma volume occurs to accommodate the demands of the growing fetus and placenta, as well as to prepare for the blood loss during delivery. As the plasma volume expands, it dilutes the concentration of red blood cells (RBCs), which can lead to a decrease in hematocrit and hemoglobin levels, a condition commonly referred to as physiologic anemia.

Understanding this concept is crucial because it reflects the body's natural adaptation to pregnancy rather than any pathological issue. This phenomenon is generally not indicative of iron deficiency or a decrease in RBC production, but rather a normal and expected response to the increased burden placed on the circulatory system during pregnancy. The increase in plasma volume allows improved circulation and nutrient delivery to both the mother and fetus, highlighting the body’s ability to adjust to these new physiological requirements.