Which physiological change in pregnancy increases the risk of urinary tract infection?

During pregnancy, there is mechanical compression of the ureters by the enlarging uterus, leading to ureteral dilation (hydroureter) and hydronephrosis. This results in urinary stasis, which creates a favorable environment for bacterial growth, significantly increasing the risk of urinary tract infections. Additionally, progesterone-induced smooth muscle relaxation further decreases ureteral peristalsis, compounding urinary stasis. These changes combined make ureteral compression and dilation the primary physiological factors increasing UTI risk in pregnancy.

Reference: Williams Obstetrics, Cunningham, 25th Edition.