Ovarian reserve is a term that refers to a woman's current supply of eggs. The number of remaining eggs is an important indicator of a woman's reproductive potential. The greater the number of eggs, the better the chance of pregnancy; likewise, a low ovarian reserve indicates a lower pregnancy rate. It is important to note that while ovarian reserve testing may tell us the quantity of remaining eggs, it doesn't tell us much about the quality of the eggs.
Methods of Ovarian Reserve Testing
A woman's age is perhaps not only the simplest but also the most important way to assess her reproductive potential. However, age alone isn't the only factor to consider. There are more involved and sophisticated methods to assess a woman's fertility potential. Passive testing methods involve the measurement of hormone levels during a predetermined baseline period. Dynamic testing methods involve hormone stimulation through injection. Specific tests for both methods are mentioned below:
Passive ovarian reserve testing
- Measuring FSH and LH
- Measuring estradiol
- Measuring Inhibin-B
- Measuring ovarian volume
Dynamic ovarian reserve testing
- Clomiphene citrate challenge test
- Gonadotropin-releasing hormone agonist stimulation test
Measuring FSH & LH
Follicle stimulating hormone (FSH) is responsible for the production of mature eggs in the ovaries. As a woman gets older and her egg supply is being depleted, the pituitary gland senses a low estrogen level. The brain signals the pituitary to make more FSH so that it can stimulate the ovaries to produce more eggs and estrogen. Elevated FSH levels indicate that the body is trying to produce follicles — something that is not necessary with younger women who have a healthy egg supply.
Cycle day 3 FSH testing serves as a baseline for comparing FSH levels on day 3 of a woman's menstrual cycle. A woman's FSH level is taken through a blood draw from a vein in her arm. While the FSH normal range may vary from one lab to another, typically FSH levels less than 15 mIU/ml have a better chance at IVF than FSH levels between 15 mIU/ml and 25 mIU/ml.
Measuring luteinizing hormone (LH) levels is also important in ovarian reserve testing but FSH levels may be a better indicator. As a woman advances towards menopause, FSH levels rise faster and quicker than LH levels. There may be added value for combined FSH and LH testing and looking at the tested levels as an FSH:LH ratio.
Measuring Estradiol
Measuring estrogen levels (specifically estradiol, or E2) on day 3 has not revealed a clear association between E2 levels and IVF outcome. Some studies have shown that measuring E2 and FSH levels together provided a more accurate assessment of ovarian reserves than using either measurement alone.
Measuring Inhibin-B
Inhibin-B is a protein hormone that is produced in the ovaries and suppresses FSH which is responsible for follicle development. Levels of Inhibin-B decreases with age and is not normally found in post-menopausal women. The amount of Inhibin-B in a woman's blood directly correlates to the quantity of eggs in her ovaries. Day 3 Inhibin-B testing is conducted similar to day 3 FSH testing—through a blood test. A normal reading from day 3 Inhibin-B testing is anything above 45 pg/mL and an abnormal reading is anything below 45 pg/mL.
Low levels of Inhibin-B is directly related to infertility. Low levels of this hormone are associated with impaired ovulation, decreased success with IVF, lower pregnancy rates, and increased risk of miscarriage.
Measuring Ovarian Volume
Ovarian volume assessment is done through transvaginal ultrasound. This technology allows a physician to measure the length, width, and depth of each ovary in order to calculate ovarian volume. The smaller a woman's ovary, the older she is in “reproductive years.” If a woman's ovarian volume is 5 mL, she would have a reproductive age of 40. A volume calculation of 7 mL would indicate a reproductive age of 30.
Medical studies have correlated ovarian volume with a woman's ability to respond to fertility medication. Women with larger ovaries tend to respond better to fertility medication than women with smaller ovaries. Additionally, larger ovarian volume seems to indicate better IVF pregnancy rates.
Clomiphene Citrate Challenge Test
The clomiphene citrate challenge test (CCCT) involves the injection of clomiphene (Clomid or Serohene). This hormone is used to trick the ovary into egg production to see if there is enough Inhibin-B or E2 to suppress both FSH production and the effects of clomiphene.
CCCT is done by first measuring day 3 FSH and E2. On cycle days 5 through 9, 100mg of clomiphene is administered and FSH and E2 measurements are taken again on day 10. High levels of FSH on day 10 is an indicator of poor ovarian reserve.
Gonadotropin-releasing Hormone Agonist (GnRH-a) Stimulation Test
Another dynamic ovarian reserve test is gonadotropin-releasing hormone agonist stimulation test (GAST). GAST is conducted by administering leuprolide acetate (Lupron) on cycle day 2 and 3 to observe changes in E2. Research has found that higher levels of E2 correspond to higher pregnancy rates. The administering of GAST involves the initial injection of Lupron and several subsequent blood tests to track E2 levels. Considering the invasive nature of this test and the costly GnRH-a injection, this is not a commonly used test.
Summary
There are many methods to estimate a woman's ovarian reserve. It is recommended that any test results indicating low or limited ovarian reserve should be followed up with further testing in future months. Ovarian reserve can differ over time so it is best to confirm results with additional testing. Consult with your physician to see which test or tests would be best suited for and most beneficial to you.
