Final answer:
During pregnancy, the uterus compresses the urinary bladder, causing frequent urination.
Step-by-step explanation:
In pregnancy, the downward pressure of the uterus compresses the urinary bladder, leading to frequent urination. This discomfort is exacerbated by increased urine production. The maternal urinary system also processes both maternal and fetal wastes, which further adds to the total volume of urine.