## Core Concept
Tocolytic agents are used to suppress premature labor by relaxing the uterine smooth muscle. These agents can have various side effects due to their mechanism of action and effects on smooth muscle and other systems.

## Why the Correct Answer is Right
The correct answer, , is associated with the use of tocolytic agents, particularly those that are beta-2 adrenergic agonists like ritodrine. Beta-2 agonists can cause **pulmonary edema** as a significant side effect. This occurs due to the increased vascular permeability and fluid shifts caused by these agents. Pulmonary edema is a well-recognized and potentially life-threatening complication.

## Why Each Wrong Option is Incorrect
- **Option A:** is not directly associated with the common side effects of tocolytic agents in a way that makes it stand out as the correct answer in this context.
- **Option B:** might relate to some side effects but is less directly connected to the well-known risks of tocolytic therapy compared to pulmonary edema.
- **Option C:** could be a side effect but is not as prominently associated with tocolytic agents as pulmonary edema.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that **beta-2 agonists**, a class of tocolytic agents, can cause significant maternal side effects, including **pulmonary edema**, **tachycardia**, and **hypokalemia**. Monitoring for these side effects is crucial when using these agents.

## Correct Answer Line
**Correct Answer: D. Pulmonary edema.**