## Core Concept
During pregnancy, the female body undergoes numerous physiological changes to accommodate the growing fetus. These changes affect various systems, including the urinary system. The bladder undergoes several modifications due to the mechanical pressure exerted by the expanding uterus and hormonal influences.

## Why the Correct Answer is Right
The correct statement regarding bladder changes during pregnancy is related to the specific alterations that occur. One notable change is the decrease in bladder capacity and an increase in bladder compliance. The growing uterus can compress the bladder, leading to changes in its shape and function. Additionally, hormonal changes, particularly the increase in progesterone levels, can affect smooth muscle tone and contribute to bladder changes.

## Why Each Wrong Option is Incorrect
- **Option A:** If option A states that "Bladder capacity decreases," this statement is actually true. The growing uterus can exert pressure on the bladder, reducing its capacity. Therefore, this option does not represent the correct answer to the question.
- **Option B:** If option B mentions that "There is an increase in residual urine," this could be considered true as well. The pressure from the uterus and changes in bladder and urethral anatomy can lead to an increase in post-void residual urine.
- **Option C:** If option C notes that "Bladder compliance increases," this statement is also true. Increased bladder compliance means the bladder can stretch more easily, which is a change observed during pregnancy.
- **Option D:** Without the specific details of each option, if one option does not align with known physiological changes in the bladder during pregnancy (e.g., suggesting no change in bladder capacity, decrease in residual urine, or decrease in compliance), it would be incorrect based on the known effects of pregnancy on the urinary system.

## Clinical Pearl / High-Yield Fact
A key point to remember is that pregnancy can lead to urinary tract changes, including an increased risk of urinary tract infections (UTIs) and alterations in bladder sensation, capacity, and compliance. These changes are primarily due to mechanical effects of the enlarging uterus and hormonal influences.

## Correct Answer: D. Detrusor instability decreases.