Antral follicle counts is done to test the Ovarian Reserve. The Ovarian volume can be correlated with the ovarian response.Both the Ovarian Reserve and Ovarian Response are helpful in predicting how the woman would respond to stimulation drugs and thus help doctors tweak the IVF treatment protocol to get the best result.
Antral Follicles are small follicles inside the ovaries whose size may vary from 2-9mm in size. Every menstrual cycle some of the primordial follicles from the primordial follicle pool are stimulated by hormonal action to grow and develop into Antral follicles. Each of this Antral follicle has the potential to develop into a mature egg and ovulate.
The number of antral follicles gives a measure of the woman’s egg supply. It is possible to count antral follicles because of their morphology. They have a fluid filled cavity that contains the immature egg. This fluid filled cavity can be detected by high quality Ultrasound Imaging thereby making it possible to easily count them.
You can’t really count the number of egg forming cells but by counting the Antral follicles you can get a measure of the size of Ovarian Reserve. The number of Antral follicles formed in each cycle is directly proportionate to the woman’s ovarian reserve.
AFC is done on Day 2 or Day 3 of Menstrual cycle, when the follicles are just starting to grow. AFC is the sum of antral follicles in both ovaries observed with TVS during day 2/day 3 of menstrual cycle. Most studies have defined antral follicles measuring 2-10mm in mean diameter in greatest 2D plane. AFC has good intercycle reliability and inter-observer reliability and widely used.
The high specificity of a low AFC is useful for predicting poor ovarian response and treatment failure.
It is calculated by measuring each ovary in three planes and using the formula for the volume of an ellipsoid (D1XD2XD3X0.52).
It has limited reliability as requires specialised equipment and cannot be included for patients with ovarian pathology like endometriomas, large cysts etc.
As no single measure of ovarian Reserve has 100% sensitivity, a combination of biochemical tests and imaging has to been done to improve test characteristics. A prospective analysis concluded that AFC in combination with AMH predicted the ovarian response more accurately.