Options for preserving fertility in women undergoing gonadotoxic treatment

Earlier onset of menopause

The immediate outcome is fewer follicles, followed by faster loss of follicles as the patient ages than in healthy women. The average age at menopause in the general population is 51. With high-dose chemotherapy, such as what patients receive in preparation for bone marrow transplant, an 18-year-old patient could lose all her follicles at once and go into menopause immediately. A moderate dose could cause an immediate loss of follicles followed by a gradual but still accelerated loss, resulting in menopause before age 51. With low-dose chemotherapy, the loss is more gradual, but the patient will still go into menopause earlier than normal.

We cannot actually count the follicles in the ovaries of a female patient who undergoes chemotherapy, but we can measure her AMH level to assess ovarian reserve. AMH levels can drop very low soon after the gonadotoxic insult, but over 2 to 3 years they gradually come back up as the primary, secondary, and tertiary follicles start producing it again. After low-dose or moderately low-dose gonadotoxic treatment, AMH levels can return to a plateau and stay there for about 10 to 15 years, but after highly gonadotoxic treatment the plateau is much lower and does not last as long, and eventually these women go into menopause very early. Unfortunately, younger age does not protect against ovarian damage.⁸ Some girls who receive chemotherapy go into menopause before ever reaching puberty.

Of the chemotherapeutic agents, the alkylating agents are considered the most harmful to the gonads, and the damage is dose-dependent.^9–11 Cancer treatment causes primary ovarian insufficiency, or premature menopause, in about 10% to 25% of prepubertal patients and in 36% of postpubertal patients.^12–14

With radiotherapy, exposure of the ovaries to about 5 to 20 Grays is enough to cause primary ovarian insufficiency regardless of the age of the patient, and even a dose less than 2 Grays can destroy 50% of the oocyte reserve, enough to cause infertility if not immediate primary ovarian insufficiency. In addition, uterine irradiation can limit the final adult uterine volume.¹⁵ This issue should always be addressed when patients undergo radiotherapy to the pelvic area because they could have major complications in pregnancy if they do become pregnant.

GnRH analogues

GnRH analogues have been used for fertility preservation since the 1980s, although their mechanism of action and effectiveness are still debated.

How do they work? Because GnRH analogues inhibit ovarian function, in theory, they could protect the ovary through several mechanisms:

• Down-regulating ovarian function¹⁶

• Decreasing utero-ovarian perfusion^17,18

• Up-regulating intragonadal antiapoptotic factors such as sphingosine 1 phosphate

• Directly protecting developing follicles and germinal cells^17–19

• Maintaining AMH production, thus keeping primordial follicles in their quiescent state, preventing “burnout,” and preserving ovarian reserve.^6,20

In a study of these effects, prepubescent mice (age 20 days) were given either cyclophosphamide alone or cyclophosphamide plus goserelin (a GnRH analogue), while a third group (controls) received neither.⁶ At age 56 days, when the mice were in puberty, AMH levels were higher in those that received goserelin plus cyclophosphamide than in those who received cyclophosphamide alone, but at 92 days, when the mice were fully mature, AMH levels were similar across the 3 groups (Figure 2).⁶ FSH levels at 56 days were lower with goserelin than with cyclophosphamide alone, though still higher than in the control group, reflecting damage to the ovaries even with goserelin treatment. At 92 days, FSH levels were the same in the 2 groups that got cyclophosphamide and lower than at 56 days, though still higher than in the control group. The total number of follicles was lower in the cyclophosphamide groups with or without goserelin, and lower than in the control group at 92 days. The conclusion was that goserelin did not fully prevent ovarian damage in this mouse model, and that the effect was only temporary, although it did foster bone elongation.⁶

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Figure 2

Antimüllerian hormone (AMH) and follicle-stimulating hormone (FSH) levels and total follicle counts at age 56 days (A) and 92 days (B) in mice that had received cyclophosphamide (CTX) alone, CTX plus goserelin, or neither drug (controls) at age 18 days. Goserelin temporarily protected the ovaries, but the protection waned over time (*P < .05).

With permission, from Detti L, Uhlmann RA, Zhang J, et al. Goserelin fosters bone elongation but does not prevent ovarian damage in cyclophosphamide-treated prepubertal mice. Fertil Steril 2014; 101(4): 1157–1164. doi:10.1016/j.fertnstert.2013.12.028

However, in an in vitro experiment,²⁰ recombinant AMH was found to decrease the replication of granulosa cells, leading to the conclusion that if a GnRH analogue decreased damage to the developing follicles, then it could also maintain an AMH level that would prevent that initial burnout of primordial follicles, which would remain a reservoir in the ovaries.

Oocyte cryopreservation

Oocyte cryopreservation (freezing the eggs) is a relatively new technique to preserve fertility in females who have already achieved puberty. It first requires stimulation with gonadotropins for about 10 to 12 days, during which follicular development is followed with transvaginal ultrasonography. Before stimulation, the follicles measure 5 to 10 mm, and when they reach approximately 18 mm, ovulation is induced to allow the eggs to mature.

Only mature eggs at the stage of metaphase 2 can be frozen. Oocytes are retrieved under ultrasonographic guidance, with a long needle attached to a transvaginal ultrasound probe. The eggs are frozen (vitrified) and kept in liquid nitrogen, where they can be stored indefinitely. (An ordinary freezer is not cold enough.) When feasible, another option is to fertilize the eggs in vitro immediately after harvesting them and freeze the resulting embryos after they have developed for 5 days, at the blastocyst stage.

When the woman is considered cured of her primary cancer, the eggs or embryos can be thawed and the eggs fertilized in vitro, and then they can be transferred into the uterus under ultrasonographic guidance.

Oocyte cryopreservation was considered experimental until 2012, when the American Society for Reproductive Medicine lifted the experimental label.²⁴ Since then, oocyte cryopreservation in female patients undergoing gonadotoxic therapy has become the standard of care.

How many eggs should we obtain and freeze? We don’t know the magic number, and the calculation is complicated because the genetic quality of the eggs declines with the age of the patient: ie, the older the woman, the more eggs are needed to allow her to have a pregnancy. Fertility decreases with age even in healthy women, and early pregnancy loss is due in most cases to genetic abnormalities in the oocytes and embryos. At age 22, only about 5% of eggs have a chromosomal abnormality, but this increases to 22% at age 32 and 65% at age 40 to 41.

Goldman et al²⁵ calculated that at least 10 eggs are needed to provide a 75% chance of pregnancy at age 34, 20 eggs are needed at age 37, and 61 are needed at age 42. Therefore, if we can retrieve about 20 oocytes, at age 34, there would be about a 90% chance of pregnancy, decreasing to 75% at age 37 and to only 37% at age 42 with oocyte cryopreservation and in vitro fertilization. In comparison, in healthy, sexually active females not using contraception, the probability of becoming pregnant during any given menstrual cycle is only about 20% to 25%. This technique is thus very effective.

Ovarian tissue cryopreservation

Ovarian tissue cryopreservation, or freezing the ovary, is a newer method. Usually, the whole ovary is extracted and the ovarian cortex is separated from the medullary portion, which is more vascular. Next, the cortex is sectioned in small fragments and frozen in liquid nitrogen. The ovarian cortex is thawed and transplanted back into the woman after she is cancer-free.^26,27

An advantage of tissue cryopreservation is that once the ovarian tissue is transplanted back, not only can the patient possibly conceive (just as with egg preservation), but she can also produce her own estrogen and progesterone and will not need hormone replacement therapy to prevent hot flashes, bone loss, and the other consequences of menopause.

Women in primary ovarian insufficiency have very high FSH concentrations, in the menopausal range of 80 mU/mL. After ovarian tissue is transplanted back into the pelvis, the FSH level gradually comes back down to normal levels of 7 to 8 mU/mL after approximately 6 months, an interval reflecting the 120 days it takes for primordial follicles to develop into tertiary follicles, which are the ones that produce the most estradiol, which feeds back with the FSH produced by the pituitary.²⁸

In May 2021, in a report by Dolmans et al²⁹ on the effectiveness of tissue cryopreservation, almost all women who underwent the procedure recovered their ovarian function, and about 25% gave birth to a healthy child. However, most of them had to undergo in vitro fertilization to become pregnant, and a 25% pregnancy rate with in vitro fertilization is considered low. Nonetheless, this is a great outcome for patients who underwent cancer therapy. With radiation therapy, the rates of success are much lower than with chemotherapy.

Starting chemotherapy before ovarian tissue cryopreservation does not impair the chances for fertility, and it may reduce the risk of reintroducing cancer with the autotransplant. Especially for blood-borne cancers like leukemia, cancerous cells may lurk in the transplant, but 2 or 3 cycles of chemotherapy before harvesting can lower the risk.

In 2019, the American Society for Reproductive Medicine lifted the experimental label from tissue cryopreservation and now recommends it for clinical practice, particularly for prepubescent patients, for whom oocyte cryopreservation is not possible.³⁰