## **Core Concept**
Cardiac output increases significantly during pregnancy to meet the metabolic demands of the mother and the fetus. This increase is crucial for ensuring adequate perfusion of vital organs and supporting the growth of the fetus. The change in cardiac output is a key physiological adaptation in pregnancy.

## **Why the Correct Answer is Right**
The maximum rise in cardiac output during pregnancy is typically observed around **28-32 weeks of gestation**. This increase is primarily due to rises in stroke volume and heart rate. The increase in stroke volume is more pronounced and occurs earlier, while the increase in heart rate contributes to the peak cardiac output in the late second to early third trimester. This period is critical as it supports the peak metabolic demands and prepares the maternal cardiovascular system for the stress of delivery.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option suggests an earlier gestational age. While cardiac output does start to increase early in pregnancy, reaching its maximum rise too early (e.g., before 24 weeks) does not align with the physiological changes observed.
- **Option B:** This option suggests a later gestational age. Although cardiac output remains elevated, the maximum increase typically occurs before term (before 37 weeks), making this option less accurate.
- **Option D:** This option suggests a very narrow and late gestational age. While close, it does not capture the range (28-32 weeks) during which the maximum rise is generally observed.

## **Clinical Pearl / High-Yield Fact**
A key clinical point to remember is that cardiac output increases by approximately **40-50%** above non-pregnant levels by the late second to early third trimester. This increase is vital for maternal and fetal well-being and is a critical consideration in managing pregnant women with pre-existing cardiac conditions.

## **Correct Answer:** B.