What is the best explanation for a patient's increased risk of developing a urinary tract infection during pregnancy?

Increased hormone levels during pregnancy lead to changes in the urinary tract that can contribute to a higher risk of urinary tract infections (UTIs). The body produces higher amounts of hormones such as progesterone, which can relax smooth muscles, including those in the urinary tract. This hormonal change can affect the function of the kidneys and bladder, potentially leading to urinary stasis, where urine remains in the urinary tract longer than normal. This stasis can create an environment conducive to bacterial growth, thus increasing the likelihood of developing a UTI.

While other factors like bladder rigidity and fetal compression can play a role in urinary flow changes during pregnancy, the primary reason for the increased risk is the systemic effect of increased hormone levels on the urinary system.