The 5 days before and 4 days after the day of ovulation, including the day of ovulation, are called the ovulation period. The day of ovulation is 14-16 days before the next menstrual period, when the chance of conception is highest and is called the danger period; the safety period is the date other than the menstrual period and the ovulation period. After ovulation, the corpus luteum is formed, and if no pregnancy occurs, the corpus luteum gradually shrinks. The luteal phase is called the luteal phase. The time of follicular growth is not necessarily fixed for each woman, but the luteal phase after ovulation is usually a fixed 14 days, so ovulation is calculated from 14 days before the next menstrual period. During this period, women have more vaginal discharge, which is egg-white like and stretched, making it a fertile period. The period other than ovulation and menstruation is the safe period, when the chance of conception is low. However, for women with irregular menstrual cycles, there is no absolute safe period or danger period. Therefore, it is recommended that women avoid using safe periods for contraception and use safer contraception instead.