When a woman is anxious to conceive and has difficulty in doing so.... her ovarian function will be tested by means of blood investigations and a SCAN. Every cycle ovulation takes place but we cannot see an ovum so indirect evidence is a follicle which is small round compartment in the ovary.....and this ruptures and releases the ovum every month...That which releases this ovum is called a follicle...and can be seen on SCAN and the required measurement is about19 to 20mm.