Female age is a critical factor in determining the chances for getting pregnant. Increased infertility with female aging is well-documented and very common in our society. Due to the societal trend of increased numbers of women who delay childbearing for educational/career goals, delayed marriages or second marriages, we now have a significant increase in age-related infertility. Women are born with all of the eggs they will ever have. The eggs are contained in 'egg sacs' called follicles. As women age, throughout life the supply of eggs (ovarian reserve) gradually declines over time until the eggs are essentially depleted at menopause. In general, egg quality and quantity start to decline slowly starting in the early 30s, and then much faster in the late 30s and early 40s. At any given time, the number of good eggs that remain is very dependent on the woman's age plus other factors, such as genetics and previous ovarian surgeries.
Despite significant advances in infertility treatments over the past 2 decades, age-related infertility remains as one of the most difficult challenges for reproductive endocrinologists (REs). Advancing age leads to a diminished 'ovarian reserve' (supply of eggs) ... resulting in a decrease in both oocyte (egg) quantity and quality. Poor egg quality results in poor embryo quality, which therefore reduces the chances for becoming pregnant successfully. In addition, as maternal age increases, the rate of miscarriage also increases substantially, as does the chance of fetal chromosomal abnormalities, such as Down syndrome.
In general, 'ovarian age' closely parallels the woman's chronological age. However, since this is not always the case, it is very important for REs and gynecologists to assess the patient's ovarian reserve of eggs. Is there a good reserve of eggs remaining in the ovaries? It is helpful to have various tests of ovarian reserve that tell us how many eggs a woman has remaining at any point in time, as well as indicating the quality of those eggs. In our field we use the term "ovarian reserve" to represent an estimate of the "reserve of eggs left in the woman's ovaries". In other words, "ovarian reserve" refers to a woman's current remaining supply of eggs, which represents her remaining fertility potential. In general, the greater the number of her remaining eggs, the better the chances for achieving a successful pregnancy. Conversely, poor ovarian reserve greatly diminishes a patient's chances for conception. In vitro fertilization (IVF) success rates start dropping for women in their mid 30s and fall significantly by late 30s, and the decline is even more substantial by her early 40s. That's why screening for ovarian reserve is such a vital part of the initial evaluation for infertility patients of any age.
OVARIAN RESERVE “EGG SUPPLY” TESTS
The following ovarian reserve screening tests are used by reproductive endocrinologists to predict a woman’s remaining ‘egg supply’:
These tests are also very helpful to predict the ability of the ovaries to respond to stimulation with injectable fertility drugs. FSH is the same hormone contained in most of the injectable gonadotropin medications that are used for ovulation induction and for IVF ovarian stimulation. These tests usually help to predict the quantity, rather than the quality of those eggs remaining… but both usually go hand-in-hand for most women.
FSH & Estrogen (FSH & E2) day 3 serum levels
By measuring a blood test for Estrogen (Estradiol) and FSH on menstrual cycle day 3 (actually it can be done on days 2, 3, or 4), we can assess a woman’s ovarian reserve of eggs. “Ovarian reserve” is based on the fact that the pituitary gland in the brain, by producing FSH, controls ovarian Estrogen production (Estradiol- E2) and the growth and development of the eggs within the follicles (egg sacs), by a mechanism called ‘negative feedback’.
If the woman's Pituitary gland 'senses' on day 2, 3 or 4 that there is a low ovarian Estradiol environment and not many egg sacs (follicles) present that month, it responds by over-producing higher levels of FSH hormone in order to stimulate the 'stubborn' ovaries to try to produce more Estradiol and stimulate follicular development. High levels of FSH (over 15 mIU/ml) are a bad sign indicating that she may have fewer eggs left. The higher the FSH, the closer she is to Menopause and therefore has decreased chances for success with IVF or any treatment, if she is using her eggs.
For women over 35, as the egg supply decreases, egg quality also worsens. However, for women under 35, with a poor ovarian reserve, the egg quality may still be adequate. This better egg quality, often seen in younger women with poor ovarian reserve ( high FSH level), helps to compensate for the decreased quantity of eggs, so they tend to still have reasonably good IVF pregnancy success rates.
Keep in mind, the FSH levels can often fluctuate from month to month… some good/some bad. However, even a single high FSH value is a 'red flag' indicating she may have a decreased 'ovarian reserve' of eggs. The ovarian reserve is usually as bad as the worst FSH measured. Women, who tend to fluctuate with their FSH levels, tend to respond to fertility medications predicted by their worst (highest) FSH values.
For the day 3 FSH assessments to be accurate, the Estradiol (E2) level needs to be below 70-80 pg/ml, since levels higher than that will artificially suppress the FSH level to the normal range. If Estradiol levels are >80, the corresponding normal FSH value can't be used as an accurate measure of 'ovarian reserve'. What we want to see on day 3 is low Estradiol and low FSH levels. In fact, consistently high Estradiol levels on d3 may be an indication of poor ovarian reserve. High levels of E2 early in the menstrual cycle (d 2-4) are often a reflection of an inappropriately advanced stage of follicular development, due to elevated FSH levels on cycle days 27, 28, and 1.
NB: Some clinicians inappropriately order just a d3 FSH level, without a corresponding E2 level. Unless E2 is also measured, this FSH level is worthless for interpretation based on the above discussion!
To summarize, the d3 measurement of FSH and E2 is a helpful test of ovarian reserve, but it’s not perfect. An abnormally high d3 FSH level (with an E2 <80), tends to accurately predict low ovarian reserve (egg quantity) and low egg quality for women over 35. However, a normal d3 FSH value does not always mean that the ovarian reserve (egg quantity) is good! There are many women with normal FSH values that have a diminished egg supply! That is why there are several other ovarian reserve tests, such as Ultrasound - Antral Follicle Counts (US-AFC), AMH levels, and CCCT, to help detect a diminished ovarian reserve problem, if one exists.
Ultrasound-Antral Follicle Counts (US-AFC)
Another reliable method for ovarian reserve testing utilizes transvaginal ultrasound (US). At the beginning of a menstrual cycle (days 2, 3, or 4), using US we can visualize, measure, and count ‘antral follicles’ (small follicles 2-9 mm in diameter), which are some of the follicles available to respond to stimulation in the ovary for that cycle. Women are born with approximately 1,000,000 microscopic inactive "primordial follicles" per ovary. Each primordial follicle contains an immature egg that may develop in the future. Each month a certain cohort (group) of follicles is available and responsive to FSH hormone stimulation from the pituitary gland. Those follicles that have been recruited each month and are growing can be seen as small antral follicles which can be measured by US.
Many studies have demonstrated that as women age, the number of these antral follicles that can be seen at the beginning of the menstrual cycle decreases significantly. Presumably, the number of antral follicles seen on US d 2-4 is indicative of the relative number of microscopic inactive primordial follicles remaining in the ovary. Therefore as women age, they have fewer eggs (primordial follicles) remaining in the ovaries, and therefore they will have fewer antral follicles seen on US.
What is considered a normal number of antral follicles, and what is considered a decreased number of antral follicles?
Anti-Mullerian Hormone (AMH)
AMH is a protein hormone produced by the granulosa cells of the growing follicles. It is first produced by the developing primary follicles after they grow from the microscopic primordial follicles. As the follicles continue to develop, AMH production is highest in the preantral and small antral follicles (<4 mm). Little if any AMH is produced by larger developing follicles (8-20mm). For this reason, the AMH levels do not fluctuate much during the menstrual cycle, so measurement does NOT have to be on cycle day 2-4, as is the case with E2, FSH and US measurements.
AMH plays a role in follicular development (folliculogenesis), regulating the formation of primary follicles from primordial follicles. Since AMH is only produced by the small developing follicles, blood levels correlate well with the size of the pool of remaining microscopic primordial follicles. AMH levels are therefore a reflection of the ovarian reserve- the remaining supply of eggs. An AMH level < .3 ng/ml indicates a very poor ovarian reserve with a poor prognosis. Levels .7 to 1.0 are low normal and levels over 1.0 are considered normal.
As women get older, the size of their remaining pool of microscopic follicles decreases. This is reflected in a decrease in both the AFC on US, as well as AMH blood levels.
Levels of Inhibin B are another measure of ovarian reserve, since this protein is also secreted by the granulose cells of the developing follicles.
Clomiphene Citrate Challenge Test (CCCT)
On d 3, serum levels of E2 and FSH are determined. Then, Clomiphene Citrate (Clomid) is administered 100 mg x 5 days from d 5-9. On d 10, FSH levels are rechecked.
The CCCT is based on the fact that administration of Clomid stimulates an increased release of FSH early in the cycle, which then stimulates follicular development, causing an increase in E2 and Inhibin levels, if follicular activity is normal. The increased Inhibin and E2 concentrations should ‘negatively feedback’ on the pituitary, resulting in suppressed production of FSH by d 10. Women with a normal ovarian reserve should have an FSH level on d 10 lower than on d 3, ideally with levels < 10 mIU/ml on both days. Therefore, if d3 FSH is abnormal, there is no point in performing the CCCT.
Remember, a normal d3 FSH value does not always mean that the ovarian reserve (egg quantity) is good! In some of these women with normal d 3 FSH values, the CCCT may uncover an underlying problem with diminished ovarian reserve.
However, in my clinical REI practice, I have found the US-AFC and AMH levels more helpful than the CCCT, in detecting poor ovarian reserve in women with normal d 3 E2 and FSH levels.
Summary: This paper reviews the negative impact of aging on fertility and discusses ovarian reserve definitions and physiology. A thorough discussion of the available ovarian reserve tests emphasizes the benefit of performing several tests in order to accurately assess a woman’s remaining egg supply and uncover any problems with diminished or poor ovarian reserve.
Age alone (over 40) portends a poor prognosis for a successful pregnancy. Ovarian reserve evaluation, at any age, helps to define and predict a woman’s prognosis for success. Decreased ovarian reserve at any age predicts a poor outcome, and the older the patient the poorer the prognosis. For women over 37, poor ovarian reserve (egg quantity) usually implies poor egg quality... and poor pregnancy rates are expected. For example, women 44 and older, doing IVF using their own eggs, have a live birth rate of less than 1-2% and should be offered donor egg options in addition to IVF. On the other hand, women under 35, with a poor ovarian reserve, have fewer eggs than normal, but may still have some good quality eggs remaining. They may still achieve reasonable IVF pregnancy success rates (although lower than normal for their age).
When ovarian reserve testing reveals a diminished or poor ovarian reserve, the best course of action is an open, honest, frank, yet compassionate discussion of prognosis for success and all available treatment options.