Question

Which metabolic derangement is normally seen in pregnancy?

• A. Metabolic acidosis
• B. Metabolic alkalosis
• C. Respiratory acidosis
• D. Respiratory alkalosis

Hint:

Progesterone drives hyperventilation, so CO2 falls.

Answer 1

The Correct Option is D

Step 1: During pregnancy, progesterone stimulates the respiratory centre, causing increased ventilation (hyperventilation) from early in gestation.

Step 2: Hyperventilation blows off carbon dioxide, lowering arterial pCO2. A fall in pCO2 raises blood pH, producing a respiratory alkalosis. So the answer is option d.

Step 3: This is a chronic respiratory alkalosis, which the kidneys compensate for by excreting bicarbonate, keeping the pH near normal. The disturbance is respiratory (driven by the lungs/CO2), not metabolic, so options a and b are wrong. Because CO2 is lowered rather than retained, there is no respiratory acidosis, so option c is wrong.

Step 4: Hence the normal acid-base picture of pregnancy is a compensated respiratory alkalosis.