The safety period is divided into the pre-ovulatory safety period and the post-ovulatory safety period. For women with a regular menstrual cycle, the pre-ovulatory safety period is from the clean period to 3 days before the start of ovulation, and the post-ovulatory safety period is from the first day after the end of ovulation to the day before the next menstrual period. Under normal circumstances, a woman’s menstrual cycle is divided into menstrual period, ovulation period and safety period. For women who have a regular menstrual cycle, i.e. one period in 28 days, their ovulation day is usually 14 days before the next menstrual period, and the 5 days before and 4 days after the ovulation day are the ovulation period. After ovulation and menstruation, the remaining time is the safe period. However, the safe period is only a relative date. Sometimes, if a woman is stimulated by external factors, such as mental stress, fatigue, staying up late, nutrition and other factors, the ovaries may ovulate early or delay ovulation, so it is possible to have intercourse during this period, but the chances of unwanted pregnancy are small. It is recommended that even if women have intercourse during the safe period, they should still use good contraception to avoid unwanted pregnancy.