Assessment of ovarian reserve by antral follicle count
A third reliable method for ovarian reserve testing also uses transvaginal ultrasound. This method is known as the antral follicle count.
Follicles are the name given to the small ovarian cysts that contain eggs. At the beginning of a menstrual cycle, using ultrasound we can visualize and even measure these follicles in the ovary. A normal follicle will be less than 9 or 10 mm in diameter.
Studies have now demonstrated that as a woman ages, the number of these follicles that are visible at the beginning of the menstrual cycle decreases significantly. It likely represents a decrease in the number of vialbe eggs that remain in the ovary.
In addition, younger women with decreased ovarian reserve may also have a smaller number of these follicles. This is demonstrated by the fact that women with a diminished antral follicle count respond poorly to fertility medications, have a greater likelihood of having IVF cycles cancelled for poor response, and when they do complete IVF cycles, their pregnancy rates are lower.
Studies differ on the exact number of follicles that would be considered decreased but most would be in agreement that a total number of less than four is very low and therefore predictive of decreased ovarian reserve.