Generally, the follicle size is 21*18mm and it will take about 1~2 days to be discharged, but there will be individual differences. Regular ovulation in fertile women is a necessary condition for conception, women with regular menstrual cycles, ovulation occurs about 14 days before the next menstrual period, when the ultrasound monitoring suggests that the follicle size of about 21*18mm has reached the dominant follicle, about 1 to 2 days to be discharged, or may be discharged on the same day, at this time you need to monitor the follicular development every day, you can be relatively accurate in the estimation of the time of ovulation. Intercourse during ovulation can significantly increase the chances of conception, and fertilization occurs within 24 hours after ovulation. When ultrasound monitoring suggests the presence of dominant follicles, as sperm can survive in women for about 2~3 days, so at this time you can arrange to have intercourse once every 1~2 days to improve the chances of conception.