The safe period refers to the period when a woman is not prone to pregnancy after having intercourse. For women who have a regular menstrual cycle, i.e., a period of about 28 days, the safe period is the period from when the period is clean to three days before the start of ovulation, and from the first day after ovulation to the day before the next menstrual period. When a woman has her period during puberty, ovulation usually occurs in the ovaries, and if the egg and sperm are able to combine, pregnancy can occur. If the egg and sperm are able to unite, the woman will be able to get pregnant. Since no egg is released during the safe period, a woman will not get pregnant after having sex at this time. For women with irregular menstruation, accurate detection of the safe period is usually recommended by ovulation test or pelvic ultrasound. For women who do not want to get pregnant, it is not recommended to use contraception through the safe period, which is prone to failure, and should use condoms and other contraceptive measures, which are generally less prone to pregnancy and less likely to cause harm to women. In addition, if a woman is affected by external factors, such as staying up late, nervousness, etc., can make some women change before ovulation, then the safety period can also change.