Women with regular menstrual periods have one period in about 28-30 days. The safe period is between days 1-7 of the menstrual cycle and the last 4-5 days of the cycle. Most couples use methods such as basal body temperature measurement and cervical mucus observation to identify the “fertile period” and the “safe period” and choose to have intercourse during the safe period for the purpose of contraception. This is because the ovaries do not ovulate during this time, and even if ovulation has occurred, the eggs are basically dead and the chances of conception are extremely low, so it is called the safe period. Although safe period contraception is easy to use, sometimes it is not safe because ovulation is affected by mental factors, environmental factors and changes in lifestyle. Therefore, for couples who have irregular menstrual cycles and live apart for a long time, the safe period method is not suitable. In addition, although the chance of conception is low during the safe period, it is still necessary to take condoms, take birth control pills or place birth control rings for double insurance.