Fall in haematocrit value observed during pregnancy is because of?

Appeared in: HPSSC Staff Nurse - 2021

Explanation

During pregnancy, the plasma volume expands significantly, by about 40-50%.
The red blood cell (RBC) mass also increases, but to a lesser extent, around 20-30%.
This disproportionate increase in plasma volume compared to RBCs leads to a dilution of the blood, a state known as haemodilution.
This physiological haemodilution is the direct cause of the decrease in hematocrit and hemoglobin values, often termed 'physiological anemia of pregnancy'.

Option B: Hemoconcentration is the opposite of haemodilution. It involves a decrease in plasma volume relative to red cells, which would cause the hematocrit to increase, not decrease.
Option C: Blood loss is a pathological cause for a drop in hematocrit. The question refers to the normal, expected physiological fall in hematocrit observed during a healthy pregnancy.
Option D: While progesterone is a crucial hormone for maintaining pregnancy, its primary functions do not include directly regulating the balance of plasma volume and red cell mass to cause haemodilution.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Physiological hematological changes during pregnancy as background academic context rather than a clinical decision trigger.
It is crucial for nurses to differentiate the normal physiological fall in hematocrit from pathological anemia (e.g., iron-deficiency anemia), which requires investigation and treatment.
Routine prenatal care includes monitoring hemoglobin and hematocrit levels, typically at the first visit and again around 28 weeks, to ensure the drop is within the expected physiological range.
This physiological hypervolemia and haemodilution protect the mother against the adverse effects of blood loss during delivery.

How to Approach the Question

First, identify the core concept of the question, which is about a physiological change during pregnancy.
Focus on the specific parameter mentioned: a 'fall in haematocrit value'.
Recall the key hematological adaptations in pregnancy. Both plasma volume and red blood cell mass increase.
Remember the key differentiator: the increase in plasma volume (40-50%) is much greater than the increase in red blood cell mass (20-30%).
Connect this disproportionate increase to its definition: haemodilution.
Evaluate the other options to confirm your choice. Hemoconcentration is the opposite process. Blood loss is a pathological, not physiological, cause. Progesterone is not the primary driver of this specific volume change.

Concept Tested & Keywords

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E6 Medicine Harrison 22e Part 2 p. 1806-1808

E6 Obstetrics Williams p. 44-63

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