## **Core Concept**
The risk of pyelonephritis is increased in pregnancy due to several physiological and anatomical changes. These changes include ureteral dilation, decreased ureteral peristalsis, and an increase in the capacity of the renal pelvis and ureters. These modifications are primarily caused by the mechanical effects of the enlarging uterus and hormonal influences.

## **Why the Correct Answer is Right**
The correct answer, **C. Ureteral dilation and decreased peristalsis**, is right because during pregnancy, the enlarging uterus can compress the ureters, leading to dilation. Additionally, hormonal changes, particularly the increase in progesterone levels, cause smooth muscle relaxation, which results in decreased ureteral peristalsis. These changes lead to urine stasis, which increases the risk of bacterial colonization and subsequent infection, including pyelonephritis.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While changes in bladder capacity and sensitivity do occur during pregnancy, they are not the primary factors increasing the risk of pyelonephritis.
- **Option B:** Vesicoureteral reflux can increase the risk of urinary tract infections, but it is not the most direct or common factor related to pregnancy that increases the risk of pyelonephritis.
- **Option D:** Increased fetal pressure on the bladder might contribute to urinary changes but is not the primary reason for the increased risk of pyelonephritis.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **asymptomatic bacteriuria** is more common in pregnancy and, if left untreated, significantly increases the risk of developing pyelonephritis. Screening for asymptomatic bacteriuria is recommended in pregnant women, typically between 12 to 16 weeks of gestation.

## **Correct Answer:** C. Ureteral dilation and decreased peristalsis