The safe period is the phase of a woman’s menstrual cycle when she is not ovulating, and the ovulation phase is the phase of the menstrual cycle when the follicles mature and are expelled. During the entire menstrual cycle, the beginning of the menstrual period is the stage of follicle development, and the follicle usually matures in about two weeks. Normally, a woman’s menstrual cycle lasts for 20 days on average. The 14th day before the next menstrual period is the ovulation day, and ovulation can occur from 3 days before to 3 days after the ovulation day, which is called the ovulation period, and is the stage when sexual intercourse can easily lead to pregnancy. During this period, there is almost no ovulation, so the chance of pregnancy is low. Generally speaking, women who have regular menstruation have a relatively regular ovulation and safety period. In addition, the safe period may not be safe because the regularity of ovulation may be affected by various external factors. Couples who want to prevent pregnancy can take other contraceptive measures such as wearing condoms, taking birth control pills or placing birth control rings are safer.