Follicles mature in about 10 days and can be found on day 3-5 of the menstrual cycle and grow to their maximum size by about day 14. A mature follicle is not considered a mature follicle until it is 18mm in diameter or more. Mature follicles are characterized by a round or oval shape with a diameter of 18-25 mm. On ultrasound examination, the mature follicle is visible as an image of a mound before ovulation, with short strong echogenicity in the proximal wall of the follicle. A mature follicle is a prerequisite for normal conception. If the follicle is poorly developed and does not grow to a normal size, it will not ovulate normally or the quality of the expelled eggs will be poor and conception will not occur normally. If a woman has poor ovarian function, or suffers from polycystic ovary syndrome, insufficient estrogen production, or low follicle stimulating hormone levels, this will result in undergrown follicles.