## **Core Concept**
Cardiac output (CO) is the volume of blood the heart pumps per minute. It is a critical parameter in cardiovascular physiology and is calculated as the product of heart rate (HR) and stroke volume (SV), i.e., CO = HR × SV. An increase in either heart rate or stroke volume (or both) leads to an increase in cardiac output.

## **Why the Correct Answer is Right**
The correct answer indicates that cardiac output increases by 30-50% during pregnancy. This increase is essential to meet the metabolic demands of the mother and the fetus. The increase in cardiac output is primarily due to an increase in stroke volume and heart rate. This physiological adaptation starts early in pregnancy, peaks in the second trimester, and is crucial for ensuring adequate perfusion of vital organs and the placenta.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it underestimates the increase in cardiac output during pregnancy. While there are individual variations, a 30-50% increase is a well-established physiological change.
- **Option B:** This option suggests a much higher increase than what is physiologically accurate for a typical pregnancy. Increases of 100% or more are not standard and could indicate pathological conditions.
- **Option D:** This option suggests no change or a negligible increase, which contradicts the established physiological increase in cardiac output during pregnancy.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that cardiac output increases significantly during pregnancy, peaking around 28-32 weeks of gestation. This increase supports the higher metabolic rate and the needs of the growing fetus. Clinicians must consider these changes when evaluating and managing pregnant patients, especially those with pre-existing cardiovascular conditions.

## **Correct Answer:** C. 30–50%