By Robert W. Rebar, MD

Professor and Chair, Department of Obstetrics and Gynecology, Western Michigan University Homer Stryker M.D. School of Medicine, Kalamazoo, MI

Dr. Rebar reports no financial relationships relevant to this field of study.

It has been known for many years that fertility begins to decline after age 35 and particularly after age 40. Together with this decline in fertility is an increase in the incidence of miscarriage, largely because of an increase in aneuploid embryos.1 However, these data hold for populations and not individuals: It has been difficult to predict when decreased fertility begins in any single woman and when she will become menopausal. Despite the ambiguities associated with the end of reproductive life, clinicians often are asked for advice and information about fertility potential. It is also known that the numbers of oocytes in a woman’s ovaries are maximal at about 24 weeks in utero and decrease from that time forward.2-4 Utilizing these bits of information, investigators have attempted to develop screening tests to measure the term “ovarian reserve.” It is important for clinicians to understand the usefulness and limitations of these screening tests and to be able to interpret the results for themselves and their patients.

Just What Is Ovarian Reserve and Diminished Ovarian Reserve?

Personally, I find the term “ovarian reserve” itself confusing. It is intended to convey some estimate of both the number and quality of oocytes remaining in the ovaries and their capacity to result in a live-born infant.5 However, measures developed to date really provide an estimate of the numbers of oocytes only and not of individual oocyte quality. The term “decreased or diminished ovarian reserve” (DOR) is intended to describe women with regular menses whose fecundability (ability to achieve pregnancy) is decreased compared to women of similar age. In reality, DOR can only be assessed by determining what transpires after the test is administered. Some studies have used response to ovarian stimulation and others have reported subsequent pregnancies. It is clear that all the tests developed and used to date are mere surrogates attempting to estimate ovarian reserve. Thus, the term DOR may refer to any of three related but distinctly different possibilities: oocyte quality, oocyte quantity, or reproductive potential.

What causes DOR? Most of the time, the cause or causes of DOR are unknown. It may be that many of those relatively young women with DOR really represent just the end of the normal bell-shaped curve; it also may be that such women have pathological processes yet to be identified. We know that certain genetic abnormalities (of which monosomy X and the fragile X premutation are the most well recognized), chemotherapy, radiation exposure of the ovaries, and cigarette smoking clearly lead to accelerated atresia and DOR.5 To this day, it is not known if the sequence of events preceding ovarian failure is the same in women approaching menopause and in those with pathological process, but it is presumed that such is the case.

What Tests Have Been Used to Assess Ovarian Reserve?

Soon after the development of immunoassays for measurement of reproductive hormones, it became apparent that menstrual cycles changed prior to menopause. One of the changes noted was a shortening of the menstrual cycle, largely due to a shortening of the follicular phase.6,7 This shortening of the follicular phase is accompanied by increased follicle-stimulating hormone (FSH) levels and by increased circulating estradiol levels in the early follicular phase. We now recognize that these changes are due to changes in the secretion of the glycoprotein hormones inhibin B and anti-Müllerian hormone (AMH), which are secreted by small ovarian follicles. (Inhibin B is secreted primarily by preantral follicles and AMH by primary, preantral, and antral follicles.) As the number of ovarian follicles decreases with age (or as a result of some stimulus such as radiation accelerating destruction), both AMH and inhibin B concentrations decrease. Decreased feedback to the hypothalamic-pituitary unit by the decreased inhibin B leads to increased FSH secretion in the late luteal and early follicular phases — and to the shortened follicular phases. Thus, FSH together with estradiol levels8 during days 2-4 of the menstrual cycle, inhibin B levels,9 and AMH levels10 all have been used to estimate ovarian reserve. Recently, using data from a cohort study of 266 women, it has been reported that serial AMH levels can be used to predict the age of menopause in individual women.11 However, this is both time consuming and costly and still does not predict the ability to conceive as menopause is neared. Moreover, this small study remains to be confirmed in a prospective trial.

One of the early dynamic tests used to assess ovarian reserve was the so-called clomiphene citrate challenge test (CCCT). In the CCCT, serum FSH is measured on cycle day 2-4 and on cycle day 10 of treatment with clomiphene citrate (100 mg daily) administered on cycle days 5-9.12 An elevated FSH level before clomiphene administration suggests DOR. So, too, do increased FSH levels compared to normal age-matched women after clomiphene administration. This is because the smaller numbers of follicles that can be recruited in women nearing the end of their reproductive lives secrete less inhibin B and estradiol with less suppression of FSH secretion in response to clomiphene.

With improvements in ultrasound, it has become possible to examine direct changes in the ovary. Thus, one popular test is the antral follicle count (AFC) and another is ovarian volume.13 The AFC describes the total number of follicles measuring 2-10 millimeters in diameter that can be seen during a scan in the early follicular phase in both ovaries. This number correlates with the number of oocytes remaining in the follicular pool and with the number of oocytes retrieved following stimulation. Obviously, ovarian volume decreases with age and also should correlate with ovarian reserve.

How Have These Tests Been Assessed and How Effective Are They?

Originally, ovarian reserve tests were intended to be used to screen women before they would begin a cycle of in vitro fertilization (IVF) to identify those women likely to respond to exogenous ovarian stimulation and to have good odds of becoming pregnant with treatment (because of the maturation and availability of several oocytes). The difficulty is that some centers have performed ovarian reserve tests on women with little likelihood of becoming pregnant, such as older women, and others have screened general populations of women seeking IVF, intending to discriminate those with good prognosis of conceiving with IVF from those with poor prognosis. Some studies have defined DOR on the basis of the response to exogenous ovarian stimulation and others have used pregnancy as an endpoint. Yet, now the usage of these tests has expanded to screen women who wish to have some estimate of their future fecundability.

One major problem is the fact that virtually all of these tests vary considerably from menstrual cycle to menstrual cycle.5 Moreover, none of these tests predicts whether pregnancy is possible, even spontaneously. In addition, when considered statistically, the best predictor of future pregnancy remains the age of the woman. Evidence of DOR does not necessarily equate with the inability to conceive.

A Practice Committee Guideline from the American Society for Reproductive Medicine notes that a single FSH value has very limited reliability because of inter- and intra-cycle variability.5 Moreover, the guideline notes that there is fair evidence to refute the notion that ovarian response and pregnancy rates will improve in cycles in which the early follicular phase FSH value is normal in women in whom a previously elevated level was recorded. Similarly, the evidence does not support the use of basal estradiol concentrations as a single screening test for DOR; however, estradiol levels do help with the interpretation of basal FSH levels. The guideline suggests that CCCT improves sensitivity for detecting DOR only mildly. It further suggests that the evidence is “mounting” to support the use of AMH as a screening test for poor ovarian response to gonadotropin stimulation. However, there is insufficient evidence to suggest it can be used to predict inability to conceive. Again similarly, the evidence that low antral follicle count (< 6) can be used as a screening test for poor ovarian response is fair, but there is insufficient evidence to support the use of AFC as a screening test for failure to conceive. There also is fair evidence that inhibin B and ovarian volume are not good screening tests for DOR. The guideline also notes that there is insufficient evidence to indicate that the combined results of multiple screening tests are more useful that any test separately. The guideline concludes by suggesting that the evidence indicates that there will be more false-positive test results as more low-risk women are tested.

What Conclusions Can We Reach about Ovarian Reserve Testing?

So what does all of the evidence mean? It means that these tests have very little value in providing predictions regarding the possibility of future pregnancy for individual women. It means that we are likely to worry more normal women unnecessarily when suspicious results are obtained on ovarian reserve testing of large numbers of women. I would suggest that ovarian reserve testing should not be used indiscriminately, but rather should be limited to women in whom there is concern about their fecundability. Tests may well be offered to cancer survivors after radiation and/or chemotherapy and to women with a family history of early menopause or various genetic mutations known to affect fertility. Ovarian reserve testing also may be appropriate for women with severe endometriosis or a history of prior ovarian surgery. Tests can be offered to infertile women older than age 40 years considering in vitro fertilization to help them determine if the expense and commitment are justified. For those normal women who are compelled to cryopreserve their oocytes because of the absence of a suitable partner or some other reason, an argument also can be made for ovarian reserve testing prior to ovarian stimulation. On the other hand, there also is one theoretical study suggesting that oocyte cryopreservation is most efficient when performed at 38 years of age.14 Almost all women are fertile until that age.

Ovarian reserve testing actually creates more questions than answers. Providing nuanced explanations to patients is difficult and challenging. These observations lead to the obvious final conclusion: Use these tests with caution — and in limited scope. A committee opinion from the American Society for Reproductive Medicine concludes that it is important to counsel women who desire to build families about the effect of increasing age.15 Thus, women older than 35 years should be evaluated and treated after six months of failed attempts to conceive — and even earlier if there is an obvious impediment to fertility. In women older than 40 years of age who wish to conceive, immediate evaluation as well as any appropriate treatment based on the findings are warranted.

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