A total of 5 days before and after ovulation is the fertile or dangerous period, except for these 5 days of the menstrual cycle, which are all within the safe period, but coitus is not recommended during the menstrual period, so the menstrual period should also be excluded. The safe period is relative to ovulation, the further away from ovulation, the lower the chance of pregnancy during intercourse. For women with regular menstrual cycle, about 30 days, ovulation can be accurately estimated and the safe period range can be clarified accordingly, which is 7 days before and 8 days after menstruation. As for women with irregular periods, they can go to the hospital for ultrasound to detect follicles, which can accurately determine the safe period. Safe period intercourse can reduce the chances of pregnancy, but it can not fully play a role in contraception. Women’s menstruation is affected by work environment, stress and exertion, which can lead to irregular ovulation, causing early or delayed menstruation, and the safety period is not accurate. Therefore, it is best to use effective contraceptive measures when having intercourse.