Women normally have thousands of immature follicles in their ovaries. Follicles deveop in the ovaries as they approach ovulation. On CD 3 your follicles really have not started to develop yet and are expected to be immature. Women normally have thousands of immature follicles in their ovaries. Follicles deveop in the ovaries as they approach ovulation. On CD 3 your follicles really have not started to develop yet and are expected to be immature. So you would expect many immature follicles to be around 10 mm more or less. As you get closer to ovulation some of them start growing and get well over 10 mm. In a natural or Clomiphene Citrate cycle, mature follicle size is between 18 - 30 mm. If triggered with medication, these cycles are typically triggered when follicle size is between 17-26mm (dependent of the practice and IVF lab).In a gonadotropin cycle, mature follicle size is between 16 - 20 mm. These cycles are typically triggered when follicle size is between 16 - 20 mm.