## Core Concept
During pregnancy, there are significant changes in respiratory physiology, including alterations in lung volumes. These changes are primarily due to the enlarging uterus, which elevates the diaphragm, and the increased levels of progesterone, which stimulate the respiratory centers.

## Why the Correct Answer is Right
The correct answer, , states that **Functional Residual Capacity (FRC) decreases** during pregnancy. This decrease occurs because the enlarging uterus pushes the diaphragm upwards, reducing the volume of the lungs at the end of a normal exhalation. As a result, FRC, which is the volume of air present in the lungs at the end of passive expiration, decreases. This decrease can affect respiratory mechanics and gas exchange.

## Why Each Wrong Option is Incorrect
- **Option A:** - This option suggests that **Residual Volume (RV) increases**, which is incorrect. RV, the volume of air remaining in the lungs after maximum exhalation, actually decreases or remains relatively unchanged during pregnancy. The decrease in lung volumes, including RV, is due to the upward displacement of the diaphragm.
- **Option B:** - This option states that **Total Lung Capacity (TLC) increases**, which is not accurate. TLC, the total amount of air in the lungs at maximum inhalation, may remain relatively constant or slightly decrease during pregnancy due to the reduced FRC and RV.
- **Option D:** - This option claims that **Tidal Volume (TV) decreases**, which is incorrect. TV, the volume of air inhaled or exhaled during normal breathing, actually increases during pregnancy. This increase helps to meet the higher metabolic demands and to compensate for the decreased FRC.

## Clinical Pearl / High-Yield Fact
A key point to remember is that during pregnancy, **progesterone levels increase**, which stimulates the respiratory center, leading to **increased ventilation**. This increase in ventilation can cause a sensation of dyspnea (shortness of breath) even though lung volumes change relatively little. Clinically, understanding these changes is crucial for managing respiratory conditions in pregnant women.

## Correct Answer: C. Functional Residual Capacity (FRC) decreases.