An ultrasound on the 11th day of menstruation to check the follicles should be around 10 mm. If the menstrual cycle is around 28 days, a follicle on day 11 can also develop to 15 mm. If the menstrual cycle is longer, the follicles can be around 10 mm. Depending on the size of the follicle, you can make an appointment for your next ultrasound. If the follicle size is around 10 mm, you can check it every two days. If the follicles have developed to 15 mm, it is recommended that they should be checked every other day. Generally, follicles that have developed to about 18-23 mm are considered pre-ovulatory follicles. Stimulated by luteinizing hormone and folliculogenic hormone, the preovulatory oocyte is expelled along with the surrounding granulosa cells of the mound, which is called ovulation. The chances of conception can be increased by having intercourse on alternate days, 2-3 days before and after ovulation.