RNC-MNN Practice Test 2025 – Your All-In-One Guide to Mastering Maternal Newborn Nursing Certification!

The correct answer is supported by the physiological changes that occur in a woman's body after delivery. After childbirth, there is a significant adjustment in blood volume. Initially, the plasma volume increases during pregnancy to support the growing fetus, which dilutes the red blood cells, leading to a lower hematocrit.

After delivery, the body begins to return to its pre-pregnant state, and there is a decrease in plasma volume as the excess fluid is excreted or reabsorbed. This decrease in plasma volume happens more rapidly than the loss of red blood cells, particularly because there is a cessation of blood flowing through the placenta, and the body starts to concentrate the red blood cells that are still present in circulation. As a result, the hematocrit—the percentage of blood volume that is made up of red blood cells—increases during this time frame (between days 3 and 7 post-delivery).

This understanding clarifies the mechanism behind why the hematocrit rises, highlighting the importance of plasma volume changes relative to the volume of red blood cells. Therefore, the interaction of these factors directly explains why the correct choice reflects the observed increase in hematocrit during this postpartum period.