There are several reasons for the anal swelling in the fourth month of pregnancy: first, because the uterus slowly increases to produce a certain pressure on the pelvic cavity, thus forming a stimulus, the uterus will also press the rectal area resulting in anal swelling, is a normal physiological reaction, most pregnant women will have this situation during pregnancy, can not be treated; second, there may be due to pregnancy after the pregnant woman It is also possible that the anal swelling is caused by constipation during pregnancy. It is recommended to eat more light food and less spicy and stimulating food to avoid such symptoms. If you feel a tingling sensation in the anus, accompanied by irritability, worrying and other conditions, it is recommended to go to the hospital for a timely examination.