For women with regular menstruation (e.g., a 28-day menstrual cycle with a 5-day period), the safe period is usually 7 days before and 8 days after menstruation (8 days from the first day of menstruation). A woman’s menstrual cycle is divided into ovulation, safety period and menstrual period. The safe period is relative to the ovulation period, and having sex during the safe period has a lower chance of pregnancy. Sex during menstruation is also not pregnant, but it is not recommended to have sex during menstruation, as it can easily cause gynecological diseases. However, the safe period is not always safe, many reasons can change the ovulation time of women, such as certain diseases, the environment, emotions, etc., resulting in some women’s menstruation is delayed, ovulation day delayed or early, in the safe period may be pregnant, during this period with the safe period contraception, can often lead to contraceptive failure. Therefore, it is recommended that women who have intercourse during the safe period should also take contraceptive measures, such as using condoms or oral long-acting contraceptive pills to reduce the chances of pregnancy.