Homerton Fertility Centre, Homerton University Hospital, London, UK
The enormous rate of atresia of ovarian follicles will leave 10,000–25,000 at age 36 years with ovulatory potential and the rate of loss accelerates even further up to the age of menopause. The assessment of ovarian reserve is important as a guide for counseling patients regarding prognosis for pregnancy if used judiciously, roughly predict the age of menopause, help determine the protocol for ovarian stimulation. In practical terms, methods for the assessment of ovarian reserve are female age, serum concentrations of FSH and oestradiol estimated on day 2–4 of the menstrual cycle, antral follicle count (AFC), serum concentrations of anti-Mullerian hormone (AMH). Female age is an independent predictor of ovarian reserve. Although wide variations are seen, female age has the advantage of being indisputable and, particularly when used with a further parameter, is probably the most valuable predictor of ovarian reserve and prognosis for live birth. Day 3 FSH levels vary from cycle to cycle and are unreliable particularly in those <40 years old. The advantage of the antral follicle count is that it is a direct measure of the cohort of follicles available and capable of responding to stimulation. However, good ultrasound equipment is necessary and large intra-observer differences have been noted. The concentration of AMH in serum is a good indicator of the size of the ovarian antral follicle pool and consequently a good predictor of the ovarian response to stimulation. It is now widely used in counseling patients and determining the protocol for ovarian stimulation.
Ovarian reserveGerm cellsPrimordial folliclesOvulationMenopauseOocyteOvarian functionGnRHAgonistAntagonistFSHSerum estradiolAntral follicleAnti-Mullerian hormoneAMHGonadotrophinsIVFOvarian hyperstimulation
In mid-pregnancy, the ovaries of the female fetus contain approximately seven million germ cells. At birth, 1–2 million remain and such is the rate of loss of these primordial follicles that at menarche 300,000 thousand follicles survive with the potential of providing an ovulatory follicle in the reproductive years to follow. Although only 400–500 will actually achieve ovulation, the enormous rate of atresia will leave 10,000–25,000 at the age of 36 years with ovulatory potential. Over this age, the rate of loss accelerates even further up to the age of menopause.
During the reproductive life span, in addition to the enormous loss of follicles in the aging process, those that survive are exposed to a number of deleterious environmental factors that influence their reproductive potential. Due to the steady decrease in oocyte numbers and an apparent deterioration in their quality in the later years, live birth rates decrease steadily with increasing age but dip alarmingly after the age of 36. In addition, the chances of a live birth over the age of 40 years are severely hindered by a greatly increased miscarriage rate due to the prevalence rate of aneuploidy, directly attributed to the remaining oocytes.
The assessment of ovarian function is important for several reasons:
· It can serve as a guide for the counseling of patients regarding the prognosis for pregnancy if used judiciously.
· It can help determine the starting dose for ovarian stimulation before the first cycle of treatment.
· It can serve to determine the protocol to be used, e.g. long GnRH agonist or a GnRH antagonist protocol.
Using a combination of female age and one or more of the examinations described below, women can be grouped into predicted low, normal or high responders and the ovarian stimulation protocol planned accordingly.
In practical terms, the following factors are used today for the assessment of ovarian reserve:
· Female age.
· Serum concentration of FSH together with serum estradiol (E2) concentrations estimated on day 2–4 of the menstrual cycle.
· Antral follicle count.
· Serum concentrations of anti-Mullerian hormone (AMH).
5.1 Female Age
The well documented deterioration in ovarian reserve with increasing female age has established age as an independent predictor of ovarian reserve. Although wide variations are seen, female age has the advantage of being indisputable and unequivocal. An upper limit is set in most countries as a cut-off point for access to treatment. Particularly when used with a further parameter, female age is probably the most valuable predictor of ovarian reserve and prognosis for pregnancy and live birth.
5.2 Day 3 FSH
The longest established biochemical predictor of ovarian reserve is serum FSH concentration. Blood must be sampled on day 2–4 of the menstrual cycle and preferably together with an estimation of serum E2 concentration. Although a reasonable predictor of ovarian response to stimulation, it is less reliable for the prognosis of attaining a pregnancy.
A detectable sign of deteriorating ovarian function is a high concentration of FSH on day 2–4 of the cycle. A level of FSH >15 IU/L is usually a bad prognostic factor for ovarian reserve, especially when associated with high estradiol concentrations (>75 pg/ml, >200 pmol/l) on the same day. Under the age of 40 years this is a much less reliable sign, especially as regards the prognosis for pregnancy, again emphasizing the importance of age for this assessment. Although still widely used, day 3 FSH estimation has several drawbacks:
· Estimations taken on day three of successive cycles often vary considerably.
· Blood sampling must be performed between day 2 and 4 of the cycle.
· Under the age of 40 years, FSH estimation is much less reliable as a predictive value.
· It is less successful than AMH and the antral follicle count in delineating poor, normal and high responders.
5.3 Antral Follicle Count
Using trans-vaginal ultrasound at the beginning of the cycle, the number of antral follicles with diameters of 2–9 mm can be counted in each ovary. In our unit a grand total of 10–15 is thought of as normal, <5 indicates a poor ovarian reserve and >15 predicts a high responder. The advantage of the antral follicle count is that it is a direct measure of the cohort of follicles available and capable of responding to stimulation. However, good ultrasound equipment is a necessity and large intra-observer differences have been noted and must be taken into account. In series comparing antral follicle count and AMH for the estimation of ovarian reserve, there is little to choose between them in terms of predictive value.
5.4 Anti-Mullerian Hormone (AMH)
Anti-Mullerian hormone takes its name from its function in suppressing the development of the female reproductive tract in the male fetus where it is produced by the fetal testes. It is, however, also produced in the ovary where maximal expression occurs in pre-antral and small antral follicles but disappears in maturing pre-ovulatory follicles. The concentration of AMH in serum is, therefore, a good indicator of the size of the ovarian antral follicle pool and consequently a good predictor of the ovarian response to stimulation. It is now widely used in counseling patients and determining the protocol for ovarian stimulation and the starting dose of gonadotrophins before the first cycle of IVF.
The initial use of AMH for the assessment of ovarian reserve was confusing due to the different assays being used but the Beckman-Coulter Gen II assay is now in general use and, following some teething troubles, is now thought to be a good indicator of ovarian reserve. In our unit, an AMH serum concentration of <5 /L indicates a poor responder, 5–20 pmol/L a normal responder, >20 pmol/L a high responder and >40 pmol/L an excessive response. Division into these groups has proved very useful for determining the protocol and starting dose of gonadotrophins to be used, as suggested by , for example, a lower treatment burden in the predicted poor responder, a maximizing approach for the normal responder and a mild stimulation protocol for the high responder can be adopted . They found the predictive value of AMH of an excessive response particularly useful in the avoidance of ovarian hyperstimulation syndrome.
Although highly predictive for the ovarian response, we are still reticent to advise against starting treatment on the strength of a low AMH concentration alone. It should be used in combination with the other factors mentioned, particularly female age, for this purpose. The AMH value is less reliable for predicting the chance of conception as several ‘surprises’ have been reported in the literature where conception was achieved despite a low AMH. It can be used as a guide for estimating ovarian reserve for women deliberating over the timing of attempting a pregnancy, particularly in the older age groups and also for those women considering social egg freezing. The value of AMH in predicting the age of menopause is still under investigation.
The estimation of AMH for the prediction of ovarian reserve has some advantages over other methods. It can be measured at any time during the menstrual cycle  and clearly delineates groups of predicted response, both of which give it superiority over FSH. As a laboratory estimation, it is not dependent on individual interpretation or specialized equipment as for the antral follicle count. Each unit should decide what works best for them as the recent literature shows that there is little to choose between the predictive value of AMH and antral follicle count .
5.5 Other Methods
Dynamic tests have also been devised to estimate ovarian reserve including stimulation with clomiphene citrate, a GnRH agonist or directly with FSH (EFORT test), all of which involve the measurement of the increment of FSH and/or estradiol increase following stimulation. These tests are now outdated following the establishment of AMH and antral follicle count in routine practice. It should be added that diminished ovarian reserve can be very simply diagnosed by a poor or absent response to a sufficient dose of gonadotrophin stimulation (in our case 300 IU FSH) while attempting treatment. This we found as a sign which even preceded the FSH rise, was the earliest sign of an impending ovarian failure and which can often be spotted during routine treatment for, so-called, unexplained infertility .
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