If you have intercourse on the first day of menstruation, you can use the following methods to reduce gynecological diseases caused by intercourse: 1. You can drink a bowl of hot brown sugar and ginger water, which can make the menstrual blood flow more smoothly, and then you can avoid the backflow of menstrual blood that causes pain in the lower abdomen or leads to endometriosis. 2. It is best to keep the vulva locally clean and take oral antibiotics for 1-2 days because menstruation is caused by endometrial shedding of Bleeding. Although you pay attention to the hygiene of coitus and do cleaning, but it is not possible to ensure that it is sterile, so the pathogenic bacteria may still enter the vagina, once there is a retrograde infection, into the uterus, it will cause inflammation of the endometrium, so you need to oral antibiotics for two days, to prevent infection.