Hello, The follicle is a functional anatomical structure which forms part of the ovary and the ovum is the cell that will mature in a microscopic part of the inner wall of a follicle over the spontaneous or stimulated ovarian cycle in normal conditions. The follicle also contains other cell types which produce estrogen required for normal development of the egg maturation. Currently, counting ovarian follicles are the truest estimate of ovarian reserve in a patient. This reserve is expressed in a number of follicles per ovary observed in the first days of the cycle (2nd to 5th) by performing a vaginal ultrasound. These follicles are called “antral”.They have been mentioned as f1,f2, etc in your scan. Ultrasound also allows us to follow the evolution and growth of follicles both in the spontaneous cycle as in a stimulated cycle fertility treatment. Depending on the number of antral follicles, a woman is considered to have an adequate or normal ovarian reserve if the count is 6-10. Low ovarian reserve, if the count is less than 6 and high ovarian reserve if greater than 12. Follicular size in this cycle phase is 2 to 10 mm. Before ovulation occurs, the average diameter of the dominant follicle is 22 to 24 mm (range 18-36 mm). It is the only marker that can predict ovulation with ease. In the stimulated cycle of IVF (hormonal treatment), generally, all or most of the antral follicles grow and they are being followed by sequential ultrasound scans. The growth rate will be different for each of them. When several of them have reached a size of about 18 mm an HCG hormone shot is given which triggers ovulation. The egg collection is scheduled 36 hours after administration of the hormone. The aim of treatment is to collect the most mature eggs that can then be fertilized by sperm to form an embryo which is later transferred in the womb. Hope I have answered your query. Let me know if I can assist you further. Take care Regards, Dr AJEET SINGH, General & Family Physician