Which CBC change is not observed during pregnancy?

• A. WBCs gradually increase
• B. Platelet counts decrease slightly
• C. Hematocrit decreases 4 to 7 points by 30-34 weeks
• D. MCV does not change

Answer: (D)

During pregnancy the body undergoes several predictable CBC changes. Blood volume expands rapidly, and plasma volume increases more than red cell mass, causing a dilutional effect that lowers hematocrit. White blood cell counts rise as a normal adaptation, with a relative neutrophilia that becomes more evident as pregnancy progresses. Platelet counts may drift downward slightly due to dilution and increased turnover, but they usually remain within the normal range. The size of the red cells, reflected by the mean corpuscular volume, does not change because pregnancy does not directly alter red cell morphology; MCV stays in the normal range unless another nutritional deficiency or hematologic disorder is present.

So, the CBC change that is not a typical pregnancy-induced change is a shift in MCV—MCV does not change.