Ovarian reserve can be assessed by counting the antral follicles thanks to an ultrasound, endocrine markers such as FSH, Estradiol, AMH and inhibin B, or thanks to a dynamic test, which investigates the ovarian response to different stimulating drugs.
Normally, the gynaecologist uses several of these methods in order to achieve a clear diagnosis. The most commonly used tests are ultrasounds and hormonal analysis.
Ultrasound and antral follicle count
Follicles are found in the ovaries and are an accumulation of spherical cells, which cover the oocyte. They are structures from where eggs originate. An antral stage follicle has a diameter of approximately 2 and 9 mm and their count provides important information about the ovarian reserve state.
This test should be performed during the follicular phase of women’s menstrual cycle, that is, between the 3rd and 5th day of the cycle.
There is another ultrasound marker, the ovarian volume, which can also provide information about the ovarian reserve. Ovarian volume also decreases with age.
As age increases, the ovarian reserve diminishes and FSH values grow.
Basal FSH levels should be measured between the 3rd and 5th day of the menstrual cycle. This indirect measurement gives us information about the size of the ovarian follicles. FSH levels above 10 indicate a low ovarian reserve.
Basal estradiol levels should also be measured during the first days of the menstrual cycle (3rd-5th). Estradiol is secreted by pre-ovulation follicles. When the number of follicles decreases, the product of the excretion between the follicles and estradiol (E2) also diminishes.
Anti-Müllerian hormone (AMH)
AMH is a glycoprotein, present in women since their 36th week of gestation until the beginning of menopause, even though it is not detectable in the blood until puberty. Its values decrease as the woman grows older.
Unlike FSH, AMH can be measured at any time during the cycle. It is the marker that best reflects, not only the patient’s response to stimulation treatments, but also her chances of getting pregnant.
AMH levels between 0.7 and 3.5 are considered normal. Levels below 0.7 indicate a low ovarian reserve.
Inhibin B concentration is inversely related to FSH values during the cycle proliferative phase. Its serum determination is a good indicator of follicular function and, indirectly, of the ovarian reserve.
Ovarian response to stimulating drugs, such as clomiphene citrate (CC) or GnRH analogues, is evaluated.
Clomiphene citrate stimulates the ovary for 5 days, normally from the 3rd or 5th day of the cycle onwards. After, the ovarian hormonal response is evaluated and controlled through ultrasounds.
GnRH analogues testing allows for changes in serum estradiol between the 2nd and 3rd day after the administration of a GnRH agonist to be measured. The normal results of this test show elevated estradiol levels.
Thanks to results obtained using these tests and assessing the patient’s age, gynaecologists can predict, to some extent, the woman’s ability to get pregnant either naturally or through assisted reproduction techniques. Results allow doctors to know how the patient will respond to the ovarian stimulation and if the treatment can be successful.
Once a woman reaches the age of 37, her ovarian reserve decreases. This can be easily observed through ultrasounds. The primordial follicles pool and the ovarian volume decrease after menopause. The ovarian volume decreases from 4,9ml to 2, 2,ml.
Clomiphene tests compare FSH and estradiol values obtained after the ovarian stimulation with basal values.
An abnormal FSH test result is indicative of a poor pregnancy prognosis and of an almost inexistent chance of pregnancy using the woman’s own eggs. This clomiphene test is one of the most widely used functional tests because it has better results and is cheaper.
It is important to keep in mind that all these tests have a prognostic value, determine ovarian reserve and do not indicate that a woman can get pregnant. These tests are very useful in assisted reproduction treatments that include a prediction of the woman’s response to ovarian stimulation.