What physiological change occurs in the urinary tract during pregnancy?

During pregnancy, one of the notable physiological changes in the urinary tract is increased smooth muscle relaxation. This occurs due to the influence of hormones such as progesterone, which relaxes the smooth muscles in the urinary system, including the ureters and urinary bladder. The relaxation leads to dilation of the ureters, making it easier for urine to flow from the kidneys to the bladder, and can contribute to increased bladder capacity as well.

This smooth muscle relaxation is essential for accommodating the growing uterus. As the pregnancy progresses, the anatomical positioning and pressure changes necessitate adaptations in the urinary system to prevent obstruction and maintain adequate urine flow. Therefore, the correct answer highlights an important physiological adaptation that supports both maternal and fetal well-being during pregnancy.

Other options do not accurately reflect these physiological changes. For instance, renal blood flow typically increases rather than decreases during pregnancy to ensure optimal waste elimination and fluid balance. Blood levels of urea tend to decrease due to increased renal clearance. While bladder capacity does increase, this does not come without some increased risk for urinary tract infections due to stasis and hormonal factors, making the statement about no risk of infection misleading.