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Why can a pregnant person appear anemic even when the body is making more red blood cells?

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Close-up of a home pregnancy test device showing a blue plus sign in the result window, indicating a positive result for pregnancy. — pregnancy Devices for individual use at home detect pregnancy by measuring levels of the hormone human chorionic gonadotropin (hCG) in urine.

During pregnancy, a person may appear to have anemia even though the bone marrow is actively producing more erythrocytes (red blood cells). This occurs because the volume of blood plasma—the liquid component of blood—increases by approximately 30 percent due to fluid retention.12

While the total number of red blood cells also increases, it only rises by about 20 percent. Because the plasma volume expands significantly more than the red blood cell count, the concentration of red cells per cubic millimeter of blood decreases. This physiological change results in a lower hematocrit and reduced blood viscosity, creating a state of "apparent anemia" that is a normal adaptation to pregnancy rather than a deficiency, provided the individual maintains adequate iron levels for hemoglobin production.1