For women with regular menstruation, ovulation usually occurs about 14 days before the next menstrual period, so it is estimated that the 4-5 days before and after ovulation are the fertile period, and the rest of the time is the safe period. The rest of the time is the safe period. A woman’s knowledge of reproductive physiology is used to predict the date of ovulation and determine the fertile period of the cycle for the purpose of contraception by abstaining from sex. However, women’s ovulation is affected by many factors, such as mental tension, environmental changes, emotional fluctuations, stressful work, life and study, and irregular lifestyle, which can cause women to ovulate before or after, or even not to ovulate, so the safety period is not very reliable and not safe.