Orthotopic Ovarian Tissue TransplantGrafting of ovarian tissue back into the body with the aim of allowing natural pregnancy to occur. It is currently the most effective technique for transplantation and has resulted in a series of live births.
Heterotopic Ovarian Tissue TransplantGrafting of ovarian tissue to another site in the body which allows easy access to the egg cells, most commonly underneath the skin of the forearm or the abdomen. As heterotopic transplantation does not involve major abdominal surgery, this approach is beneficial for patients where repeat abdominal surgery may be complicated. However, this technique does not allow for natural pregnancy and in- vitro fertilization is needed for conception. While live births from experimental heterotopic transplants performed in primates have been reported, no human births have been reported to date.
In our centre, orthotopic ovarian tissue transplantation is performed whenever feasible because of the uncertain effectiveness of heterotopic ovarian tissue transplantation in restoring fertility in humans.
Before starting on chemotherapy or radiotherapy, the patient would undergo a keyhole procedure to remove one of the ovaries. The procedure is done under general anaesthesia and lasts for about an hour. Should the patient require surgical treatment for her cancer, the two procedures may be scheduled at the same time, if feasible. After the ovarian tissue is harvested, it is prepared for storage using specialised freezing techniques known as cryopreservation.
In most cases, the transplant of the ovary tissue back into the patient's body can only take place at least two years after the end of the cancer treatment, when the cancer is in remission. Before the transplant, the stored ovarian tissue will be thawed and checked for any spread of cancer.
Given the limited lifespan of ovarian tissues, transplantation will be postponed until the patient is ready to conceive. If needed, the patient will be referred to an obstetric specialist to discuss potential pregnancy complications unique to cancer survivors
Unlike conventional organ transplants, patients undergoing ovarian tissue transplant do not need to take any long-term immunosuppressive medications after the surgery. As the ovarian tissue that is harvested and re-implanted is the patient's own, there is no risk of organ rejection.
The lifespan of the graft varies depending on the amount of tissue transplanted and the age of the patient when the ovarian tissue was first removed. Currently, it is not possible to predict how long the graft will function after transplant.
In general, the patient can expect to resume normal menstrual cycles within four to nine months after transplantation. Among women who were trying to conceive after ovarian tissue transplant, a spontaneous pregnancy rate of about 30% has been reported.
1. What are the benefits of ovarian tissue freezing and transplantation compared to the other methods of fertility preservation (e.g egg storage, embryo storage)?
Ovarian tissue freezing is a more efficient way of preserving thousands of oocytes (female egg cells) at one time, without the need for hormonal stimulation and a source of sperm. Therefore it is an ideal option for patients without a male partner and require cancer treatment urgently. In contrast, egg and embryo freezing require a period of hormonal stimulation and only allow small numbers of eggs and embryos respectively to be preserved with each treatment cycle.
Ovarian tissue freezing is also the only option for fertility preservation in prepubescent girls who need cancer treatment.
2. I have completed my family but am worried about premature menopause after completing chemotherapy. Would ovarian tissue freezing and transplant be suitable for me?
Because of the limited duration of graft function, ovarian tissue transplant is unlikely to be effective for preserving the long- term hormonal function of the ovary. Currently it should only be performed with the aim of preserving fertility. It is not recommended as a strategy for long- term hormone replacement and should not be performed to prevent premature menopause in women who do not wish to conceive after cancer treatment.
3. Are there any risks involved with ovarian tissue transplantation?
There are surgical risks involved as two operations are needed to retrieve the ovarian tissue and graft the cryopreserved tissue back into the body.
It is not possible to test the retrieved ovarian tissue for tumour cells as the testing process will destroy the ovarian tissue. There are theoretical concerns that there may be hidden tumour cells in the ovarian tissue which can be reseeded back into the body with the transplant. Therefore careful patient selection is needed and the procedure is restricted to cancer patients with a low risk of ovarian involvement. To date, we have not encountered any reports of cancer recurrence resulting from reseeding of cancer cells from an ovarian transplant.
As ovarian transplant is a relatively new procedure, there has yet to be a published report of the short- and long-term outcomes of the children conceived by this method.
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