**Core Concept**
Urinary tract infections (UTIs) are a common complication in pregnancy, affecting approximately 2-10% of pregnant women. The risk factors for UTIs in pregnancy include anatomical, physiological, and immunological changes that occur during pregnancy, making women more susceptible to UTIs.

**Why the Correct Answer is Right**
During pregnancy, the risk of UTIs is increased due to several factors, including:
* **Hormonal changes**: Relaxation of the pelvic muscles and urethral sphincter due to the increase in relaxin levels, making it easier for bacteria to ascend into the urinary tract.
* **Ureteral compression**: The enlarging uterus can compress the ureters, leading to a decrease in urine flow and increasing the risk of UTI.
* **Immune system suppression**: Pregnancy is associated with a decrease in the immune system's ability to fight off infections, making pregnant women more susceptible to UTIs.

**Why Each Wrong Option is Incorrect**
* **Option A:** **Prolonged use of catheters** is actually a risk factor for UTIs in pregnancy, as it can introduce bacteria into the urinary tract. This option is incorrect because it is a known risk factor, not an exception.
* **Option B:** **Diabetes mellitus** is not a direct risk factor for UTIs in pregnancy. While diabetes can increase the risk of UTIs in general, it is not a specific risk factor in the context of pregnancy.
* **Option C:** **Family history of UTIs** is a known risk factor for UTIs in pregnancy. If a woman has a family history of UTIs, she is more likely to develop a UTI during pregnancy.

**Clinical Pearl / High-Yield Fact**
Pregnant women with a history of recurrent UTIs or other urinary tract abnormalities should be screened for UTIs more frequently, and prophylactic antibiotics may be prescribed to prevent UTIs.

**Correct Answer:** B. Diabetes mellitus