Frequent urination symptoms that appear in early pregnancy disappear after the third trimester. However, in late pregnancy, along with the head of the fetus entering the pelvis, when the bladder is irritated by pressure, frequent urination symptoms will appear again. The frequent urination symptoms that appear in early pregnancy are caused by the enlargement of the uterus and pelvic congestion that irritate the bladder wall after pregnancy. Until the third trimester, the uterus, although gradually enlarging, is still located in the pelvic cavity, causing constant irritation of the bladder and the symptoms of frequent urination. After the third trimester, the enlarged uterus protrudes from the pelvic cavity, relieving the irritation to the bladder wall, and the symptoms of frequent urination will naturally disappear. After the first trimester of pregnancy, the symptoms of frequent urination appear again as the head of the fetus enters the pelvis. During pregnancy, the pregnant woman’s resistance to disease decreases, the vulvar area is moist, secretions increase, easy to suffer from infectious diseases of the urinary system.