## **Core Concept**
Cardiac output (CO) is the volume of blood the heart pumps per minute. During pregnancy, CO increases significantly due to various physiological changes. The increase in CO is crucial to meet the metabolic demands of the mother and the fetus.

## **Why the Correct Answer is Right**
Cardiac output starts increasing early in pregnancy, peaks in the late second to early third trimester, and then remains elevated until delivery. Specifically, CO peaks around **28-32 weeks** of gestation. This increase is due to several factors, including increases in stroke volume and heart rate. The increase in stroke volume is primarily responsible for the rise in CO early in pregnancy, while both stroke volume and heart rate contribute to its peak.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option suggests an earlier peak, which is incorrect because while CO does start increasing early in pregnancy, it doesn't peak until later.
- **Option B:** This option suggests a later peak, which is close but not the most accurate timeframe for the peak increase in CO.
- **Option D:** This option suggests that CO does not significantly change or peaks much earlier or later than the correct timeframe.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that cardiac output increases by approximately 40-50% above non-pregnant levels by the late second to early third trimester. This increase supports the high metabolic demands of the mother, fetus, and placenta. Clinicians must consider these changes when evaluating and managing pregnant patients, especially those with pre-existing cardiac conditions.

## **Correct Answer:** . 28-32 weeks