During fetal life, 100–2000 primordial germ cells enter a massive proliferation process and, by mid-gestation, there are several million potential oocytes. However, most (85 per cent) of them are lost prior to birth  (Figure 6.1).
During fetal life, 100–2000 primordial germ cells enter a massive proliferation process and, by mid-gestation, there are several million potential oocytes. However, most (85 per cent) of them are lost prior to birth  (Figure 6.1). Indeed, of around 1 million oocytes per ovary at birth, only 450 go on to be used. The decline in follicle numbers extends from birth until puberty and continues throughout reproductive life, during which time around 450 monthly ovulatory cycles occur. The majority of follicles undergo atresia during their growth phase. Cyclic folliculogenesis and ovulation, associated with massive follicle atresia and aging-induced apoptosis, subsequently result in ovarian atrophy and reduced fertility [13, 38]. Poor oocyte quality, characterized by abnormalities in the meiotic spindle, chromosome misalignment and shortened telomeres, are among various mechanisms put forward to explain decreased fertility in women over 40 years of age [13, 22, 23].
Figure 6.1 The ovarian reserve throughout a woman’s life, from conception to 55 years of age. Only around 1000 follicles remain at menopause. Donnez and Dolmans  propose ovarian tissue re-implantation when women reach the menopause. Ideally, their tissue should have been harvested and frozen at the age of 20–25 years.
Depletion of the ovarian reserve at a young age may be the consequence of medical therapy. Indeed, some cancers as well as certain benign diseases are treated by chemotherapy, often with alkylating allografting agents, considered to be the most gonadotoxic drugs [13, 15]. Ovarian surgery for severe and recurrent endometriosis is also a common cause of ovarian reserve decline, as are known risk factors for premature menopause (Turner syndrome, family history) [12, 13, 15].
At menopause, follicular density is very low. Although around 1500 primordial follicles remain, the vast majority are caspase-positive and resistant to stimulation by gonadotropins [16, 38]. According to Lobo, Amundsen and Diers, the age of menopause has changed very little over the centuries, while life expectancy has continued to climb [2, 3, 24, 27].
At the dawn of humanity, life expectancy rarely exceeded 35 years, so the ovary was designed to work for an entire lifetime. However, women now commonly live beyond 80 years, which somewhat changes the picture and begs the question: is it possible for natural ovaries, each containing several million oocytes at mid-gestation, to continue functioning until death? [15–16]
A better standard of living and improved health care have boosted life expectancy markedly over the last 100 years or so, from 48.3 years in 1900 to 80 years in 2000, essentially thanks to advances in public health measures and efforts. In the course of the twentieth century, despite a brief dip caused by the 1918 flu pandemic (Figure 6.2) , the average lifespan increased by more than 30 years (in the US and the Western world). It is predicted that 50 per cent of all girls born today will live to over 100 years of age in many parts of the world [4,5]. The consequence of this extended longevity is that much greater numbers of women will spend substantial portions of their lives in the menopause, exposing them to a high risk of diseases linked to the absence of estrogens, like cardiovascular disease and bone mineral density loss [24, 27]. Indeed, around 30–50 per cent of women aged greater than 50 years will suffer an osteoporosis-related fracture in their remaining lifetime. The medical costs of treating broken bones from osteoporosis amounts to US$18 billion a year, and loss of work adds billions more [4,5].
Figure 6.2 Life expectancy in the US.
From an economic perspective, preventing disease is vastly preferable to having to treat it. With many major chronic diseases occurring after the menopause, the goal should be to combat them not only to extend life but also enhance its quality [24, 27]. Individualization and tailor-made medical approaches remain the key.
In the 1980s, a number of studies (including meta-analyses) suggested that MHT could be beneficial for prevention of osteoporosis, coronary heart disease and dementia, thereby cutting mortality rates. In 1992, the American College of Physicians actually recommended MHT for prevention of coronary heart disease . In the early 2000s, however, several randomized trials (Women’s Health Initiative [WHI] , Million Women Study [MWS]) indicated that the risks, including for breast cancer, outweighed any benefits. This unfortunately led to the introduction of new guidelines, resulting in a 50 per cent drop in MHT use . In 2013, 10 years after the WHI, Lobo wanted to revisit the question. Reanalysing data from the original MHT trials, he concluded that women aged 50–59 years or those within 10 years of menopause showed lower rates of coronary heart disease and all-cause mortality and, notably, no increase in perceived risks, including for breast cancer [24–27]. Indeed, the relative risk for coronary heart disease was 0.65 (0.44– 0.96), for breast cancer 0.76 (0.52–1.11), and for total mortality 0.78 (0.59–1.03) [25, 27] in the 50–59-year age group taking part in the conjugated equine estrogen-alone trial of the WHI. MHT is also known to decrease the incidence of menopausal symptoms and risk of bone fractures, improving quality of life. Thus, despite an increased incidence of breast cancer in women receiving estrogen-progestin therapy, overall mortality was found to be reduced, with deaths related to cardiovascular disease or osteoporosis .
The risk–benefit balance therefore remains positive for MHT use, with risks considered rare in healthy women aged 50–60 years, something known as the ‘timing hypothesis’ [25, 27]. As suggested by Lobo  (Figure 6.3), having already come full circle with MHT since its introduction, it is now time to implement a general prevention strategy for women approaching menopause.
The literature on this topic is of course very scarce. A first paper by Callejo and colleagues  described a series of three patients undergoing hysterectomy and bilateral oophorectomy, followed by immediate re-implantation of ovarian cortical tissue in the abdominal wall. In this series, ovarian secretion had only a short reproductive span, so the authors concluded it was unlikely that heterotopic grafts would have the longevity to serve as an adequate substitute for MHT after natural menopause. Their conclusion was clearly wrong, because of the group of women involved, aged 45–49 years, as their ovarian reserve was already extremely depleted.
The second paper, by Kiran and colleagues, was a case report. A 44-year-old patient operated on for uterine fibroids had ovarian tissue (10 cortical strips) implanted above the rectus abdominis fascia . Folliculogenesis was confirmed by ultrasound 18 months later, as were low luteinizing hormone and follicle-stimulating hormone (FSH) levels. No further details on this case could be found, however, so no conclusions could be drawn.
Duration of Ovarian Activity after Re-implantation of Frozen-Thawed Ovarian Tissue in Case of Iatrogenic Menopause
Series of Donnez and Dolmans
In this series, restoration of ovarian activity with recovery of menses occurred in 100 per cent of cases . In an earlier series, ovarian function had failed to resume in three patients who were found to have no follicles in their grafted tissue [13, 14], emphasizing the importance of an intact follicular reserve. Figure 6.4 shows long-term ovarian activity in a series of five women who underwent ovarian tissue cryopreservation before the age of 22 years, followed by re-implantation some years later. Ovarian function was restored for a period of 6–7 years, as evidenced by estradiol and FSH values similar to those observed during reproductive life.
The ovaries of a newborn girl contain an average of 1 million primordial follicles, dropping to 100 000 by 20 years of age and 65 000 by 25 years . Ideally, ovarian biopsies should be taken when follicular density is high (between 20 and 25 years) because, as demonstrated by our team, ovarian function can then be restored for longer periods of time .
Series of Andersen and Kristensen
In a recent paper, Andersen and Kristensen reported that four patients underwent their first tissue transplantation procedure more than 10 years ago in their centre . Two of the women subsequently experienced ovarian activity for a period of 6–7 years.
Series of Kim
In Kim’s series, four patients aged 27–37 years had their ovarian tissue cryopreserved between 1999 and 2004 with re-implantation performed between 2001 and 2011 . Ovarian tissue slices were grafted to a heterotopic site (between the rectus muscle and rectus sheath) and long-term follow-up was initiated. While recovery of ovarian function was achieved, its duration was relatively short (3–6 months), so the patients underwent a second transplantation. In one woman, low FSH and high estradiol levels proved that the graft was still functioning 7 years later. This clearly shows that if the goal is restoring ovarian function rather than fertility, a heterotopic location (forearm, abdominal wall) could be an easily accessible and effective site for re-implantation . According to Kim [17, 18], there was progesterone secretion from the heterotopic grafts.
Taking biopsies from the ovary has little if any impact on fertility or age at menopause. Even removal of a whole ovary has been demonstrated to have a negligible effect, and it is now widely known that women with one ovary remain as fertile as women with both . Onset of menopause is also only marginally affected in these women, who tend to start their menopause around 1 year earlier [7, 39]. We may therefore state with some degree of certainty that removal of less than 30 per cent of one ovary has a minimal impact on the ovarian reserve [15, 16].
Long-term endocrine function could well persist for more than 7 years (12 years with a repeat procedure) after frozen-thawed ovarian tissue re-implantation  (Figure 6.4), and consequently prevent menopause-related conditions like osteoporosis and other symptoms of estrogen deficiency .
Thus, having proved that ovarian tissue re-implantation is able to restore ovarian activity after induced menopause, why not use it to re-establish sex steroid secretion after natural menopause? As the goal in this case is not fertility restoration, the graft site can be heterotopic, namely outside the pelvic cavity (such as the forearm or rectus muscle) (Figure 6.5). Moreover, the procedure is potentially achievable under local anaesthesia (Table 6.1). When the implants stop working surgery may be repeated and endocrine function restored for longer. Thanks to improvements in new techniques serving to hasten revascularization, follicle loss rates may be reduced, with the benefits of grafting felt sooner and for longer periods .