Follicle monitoring is done by vaginal ultrasound for infertile women to see how the follicles are developing and if there is normal ovulation. For women with normal menstrual cycles, ovulation is usually on the 14th day before the next menstrual period. The monitoring of ovulation is usually done by vaginal ultrasound every two days from day 8 of the menstrual cycle to observe the development of follicles in both ovaries. When the follicles reach 17 mm in diameter, the monitoring is changed to once a day, and when the follicles develop to 20 mm in diameter they need to be monitored twice a day until ovulation. Only follicles larger than 1 cm in diameter can be called dominant follicles and ovulation will occur with the dominant follicle. When ovulation is monitored by ultrasound, conception can be guided by intercourse.