Few practitioners would be unaware of the impact of sweeping social trends on our working and personal lives. One such trend of particular relevance to our specialty is the phenomenon of delaying starting a family that has resulted from the use of effective contraception. Women and couples have the ability to give childbearing a lower priority than other individual goals.

Fertility rates have halved since 1961. Forty years ago, the rate was 3.83 children per woman, whereas now it is only 1.81. Over the same period, the proportion of mothers aged 30 years or over has increased from 31.5 per cent to 46.4 per cent, with remarkable consequences for the prevalence and pattern of infertility. Statistics from the Wesley Monash IVF unit, like other assisted reproduction technology (ART) units in Australia, have revealed an increase in the proportion of women over the age of 37 attending our unit over the last decade. Last year, one-third of our fertility patients were in this age group.

The biological clock

Despite some groups looking for evidence of oocyte regeneration from non-ovarian progenitor cells¹, it is widely accepted that females lose the capacity for germ cell regeneration. At menarche, girls have approximately 250,000 primordial folllicles in their ovaries. Apoptosis and the cohorts of primordial follicles that contribute to ovulation steadily reduce follicle numbers each month, until the count drops to about 25,000 in a woman’s late 30s. Thereafter, accelerated losses occur until the menopause, when only a few remain. This latter period is associated with declining gamete competency and can predate menopause by more than a decade.² In ART practice, the decline in female fertility is seen as starting from age 32 and most in vitro fertilisation (IVF) units will not perform IVF on women using their own eggs from age 45 older, since the chance of a live birth is so low. Accelerated loss of ovarian reserve is seen in patients who have undergone chemotherapy or radiotherapy, those who carry a genetic predisposition and smokers.

What is the physiological basis underlying this reduction in count and quality of follicles that we call the ‘biological clock’? Declining numbers may be due to impaired follicular microcirculation, hormonal disturbances and disrupted perifollicular somatic cell function from stromal senescence³, with underlying degradation of cohesins associated with chromatid disaggregation at metaphase 1.⁴ Two separate events may explain the poorer quality of the oocyte of the older woman: reduced formation of chiasmata during fetal oogenesis; and chromatin insult secondary to reactive oxygen species damage sustained before ovulation.⁵

Investigations to establish a woman’s ovarian reserve

For the clinician the more important question is: How much time is left on my patient’s clock? What is a woman’s ovarian reserve? Over the past two decades a number of tests of ovarian reserve have been studied in the context of IVF treatment, with the outcome measures of oocyte yield and occurrence of pregnancy. Broekman’s systematic review concluded that these tests have modest predictive properties for poor ovarian response to hyperstimulation and very limited ability to predict successful pregnancy.6 Sills review published last year reached similar conclusions, but added that such tests may be useful as a screening tool and I list them below as an indication for earlier referral to an ART unit.⁷

Age

Age is still one of the best indicators of reduced number and quality of oocytes. Infertility has been defined as the inability to fall pregnant after 12 months trying for a pregnancy. In women 35 years of age or more, most ART units would encourage referral after six months of trying. This is because there is little remaining time for investigation and potential treatment, especially if more than one child is desired.

Antral follicle count (AFC)

Ovarian imaging by transvaginal ultrasound shows a reduced number of smaller antral follicles available for gonadotropin recruitment as ovarian reserve declines. The number of antral follicles with a diameter of 2 to 10 mm measured on day one or day two of the period is readily counted and this measure is widely used, formally or informally, in ART units. Other studies have counted follicles up to 6 mm. A count of less than five follicles has been linked with inability to achieve pregnancy.⁸ Prognostic usefulness is reduced by problems that include intercycle variation in results, and inter-observer differences. A meta-analysis concluded that the AFC had limited use in prediction of non-conception.⁶

Anti-mullerian hormone (AMH)

AMH is one of the intra-ovarian growth factors regulating primordial follicle recruitment and FSH-sensitivity of growing follicles in an inhibitory manner. AMH is secreted by granulosa cells, from primary, pre-antral and antral follicles up to 6 mm in size. The serum levels are unaffected by use of the oral contraceptive pill or by pregnancy. Levels are mildly reduced in obese patients and a small brief drop occurs after ovulation or IVF hyperstimulation, but inter- and intra-cycle variability is low enough to permit random timing of AMH measurement during the menstrual cycle.9 AMH is believed to be the earliest marker to change with advancing maternal age. The cost of AMH testing to the patient in Brisbane is A$60 and a result of less than 14 pmol/L is suggestive of failing ovarian reserve, while a level of greater than 30 pmol/L indicates the possibilities of polycystic ovarian syndrome (PCOS), with increased risk of ovarian hyperstimulation syndrome in a stimulated cycle, or in post-menopausal females, a granulosa cell tumour.

While AMH and antral follicle count are regarded as ‘the best’ of the tests of ovarian reserve, many IVF units may use these tests to work out starting dose of gonadotropins, but would rarely use them to refuse IVF treatment without a trial IVF cycle first.

Early follicular phase FSH levels

Elevated serum follicle-stimulating hormone (FSH) is a direct pituitary compensation for the older and less responsive ovary. Reduced follicle numbers and estradiol levels attenuate the negative feedback loop on the hypothalamo-pituitary secretion of FSH. Timing of collection is important and levels vary considerably between cycles. Values above 20 mIu/ml are associated with a pronounced decline in conceptions.10 Another study suggests that a level over 10 mIu/ml warrants earlier referral.⁷

Elevated estradiol levels

Basal levels of estradiol measured on days two or three of menstruation correlate inversely with ovarian response to gonadotrophins in patients undergoing IVF. Levels over 275 pmol/L are unfavourable.⁷ Overall, this test has low predictive value for poor response and for non-pregnancy. Other tests of ovarian reserve that have been evaluated, including the clomiphene citrate challenge test, GnRH-agonist stimulation test and ovarian biopsy, but these have not become part of standard practice.

It can be summarised that while we can predict the number of oocytes retrieved in an IVF cycle, we are still unable to test for the quality of those oocytes and the consequent pregnancy rate.

Age is still the most clinically useful measure. In a woman aged under 36, an AFC of less than 10, or an AMH level of less than 14 pmol/L, or a day two FSH of greater than 10 mIu/ml, are all suggestive of reduced ovarian reserve, with the consequent need for earlier referral. It is worth stating too that these tests have no additive effect. In essence, they are measuring the same thing, so using different tests adds little new information.

Management of age-related fertility delay

Controlled ovarian hyperstimulation and IVF does not treat the underlying problem of age, the reduced number and poor quality of oocytes. It does, however, allow the search for the ‘good’ embryo to be accelerated and many months of ‘trying’ to be sped up. Thus, IVF is currently the commonest treatment for age-related infertility. The only ART treatment that really addresses the problem of age is the use of oocytes donated from younger known or unknown, altruistic, or paid (overseas) donors.

Oocyte freezing

The advent of rapid freezing vitrification of oocytes has opened the door to more widespread oocyte freezing for the ‘social’ indication of reduced ovarian reserve. Good freeze-thaw rates of over 90 per cent, fertilisation rates of 75 to 90 per cent and pregnancy rates of 32 to 65 per cent have been reported.¹¹ Women need to be informed, however, that this technique is still experimental and the cost is considerable as Medicare funding is not applicable.

Conclusions

Inexorable social changes mean that more women are delaying childbearing. This has been a burden for IVF units and a major shock for women. Various tests are available to ‘predict’ ovarian reserve but none are perfect. At present, there is no treatment that effectively overcomes the deleterious effect of age on a woman’s fertility. The best advice is to have children young.