Freezing and Storage
WHAT’S IN THE FREEZER?
‘Cryopreservation’ in the IVF lab, commonly called ‘freezing’, is the term used to describe the process by which the viability of reproductive cells is preserved for future use by infusion with a cryo-protectant, and cooling to very low temperatures. With current technology we can now cryopreserve embryos, sperm, eggs and small tissue fragments, such as those from ovary and testis.
Since the first human pregnancy from a cryopreserved embryo was reported in 1984, the ability of embryologists to cryopreserve embryos in particular, has proved invaluable to couples undergoing fertility treatment.
WHY DO WE FREEZE EMBRYOS?
In a typical IVF or ICSI cycle, stimulation of the ovaries to produce many eggs often leads to the production of more embryos than can be safely transferred to the woman’s uterus at one time.
It is known that transferring high numbers of embryos carries a significant risk of multiple pregnancies, without increasing the singleton pregnancy rate proportionally. It is routine practice therefore to select the best one or two embryos for transfer and to cryopreserve any suitable surplus good quality embryos. These can then be thawed and transferred at a later date in the event that the fresh cycle is unsuccessful or perhaps siblings are sought.
In some circumstances, it may be necessary to postpone an embryo transfer completely and freeze all suitable embryos rather than transfer them to the uterus. Occasionally the uterine lining does not develop optimally and the fertility specialist will recommend that the embryos are frozen and transferred in another cycle when the uterine environment provides a better chance of implantation. All suitable embryos may also be electively frozen if a woman is at risk of developing ovarian hyper-stimulation syndrome (OHSS) because if she becomes pregnant, the condition has the potential to be made much more severe.
WHEN ARE EMBRYOS FROZEN?
Human embryos can be frozen on day one after insemination (pronuclear stage embryo) or at any stage up to and including the blastocyst stage (five or six days after fertilisation). At Life Fertility Clinic embryos are most commonly frozen at the blastocyst stage.
HOW ARE EMBRYOS FROZEN?
At Life Fertility Clinic, blastocyst stage embryos are frozen using the latest technique called ‘vitrification’. The embryos are infused with a cryo-protectant solution to protect them from the effects of ice crystal formation; cooled to very low temperatures; and then stored in liquid nitrogen (at -196oC).
WHAT DOES A FROZEN EMBRYO TRANSFER CYCLE ACTUALLY INVOLVE?
Frozen-thawed embryos are transferred into the uterus after the preparation of the lining of the uterus (endometrium) using either a ‘natural cycle’ or a ‘hormone replacement cycle’.
In a natural cycle, the patient will be monitored by ultrasound to determine when ovulation occurs. The embryos will then be transferred at the appropriate time after ovulation to ensure harmony between the developmental stage of the embryo and the uterine lining. During a hormone replacement cycle, appropriate development of the endometrium is achieved using a combination of hormonal medications.
In both types of cycle, the appropriate number of embryos is thawed in advance of the embryo transfer to ensure that they have survived the freezing thawing process before transfer.
ARE THERE ANY RISKS ASSOCIATED WITH EMBRYO FREEZING?
The main risk associated with cryopreservation is cell damage during the freezing-thawing process that results in embryos not surviving.
Embryo survival rates are generally highest (approx. 90%) for blastocysts that have been frozen by vitrification. Embryos frozen either at the pronuclear stage, or at the 2 to 8 cell stage are usually frozen by a slightly different technique called ‘slow freezing’ and approx 80% of these embryos survive the thawing process.
Embryo survival does however vary between patients and irrespective of the technique used or the stage at which they were frozen, it is possible that none of a couple’s embryos will survive the freezing and thawing process.
To date, there is no evidence to suggest that the freezing and thawing of embryos has resulted in an increased risk of miscarriage and congenital abnormality over that expected for natural pregnancies.
DO FROZEN EMBRYO TRANSFERS WORK?
Success rates for frozen-thawed embryo transfer cycles vary. However, the implantation rate for thawed vitrified blastocysts is approximately the same as for fresh blastocysts.
HOW LONG CAN EMBRYOS BE STORED FOR?
According to the legislation in Australia (NHMRC Ethical guidelines on the use of assisted reproductive technology in clinical practice and research, 2007), embryos may be kept for a period of up to five years, with an option to renew consent for a further five years. At the conclusion of the maximum period, and if no alternative arrangements have been made with the persons for whom the embryos were stored, the fertility clinic must remove them from storage and arrange for their disposal.
WHAT ABOUT FREEZING EGGS?
A lot of scientific research has been carried out to develop techniques to cryopreserve mature oocytes (eggs). The first baby born using frozen oocytes was in 1986. In the subsequent 15 years, only a small number of babies were born worldwide from thousands of frozen-thawed oocytes and the technology was considered largely experimental by the IVF community.
In recent years however, with the development and refinement of the technique of vitrification for the cryopreservation of oocytes, results have been improving. Life Fertility Clinic can now offer oocyte cryopreservation by vitrification in selected cases.
The ability to cryopreserve oocytes prior to fertilisation provides an option for patients undergoing IVF who may have moral or ethical objections to freezing supernumerary embryos. Cryopreservation of oocytes avoids some of the dilemmas that may be raised by the disposal of embryos.
The ability to freeze eggs also has the potential to offer options for fertility preservation to women facing premature loss of ovarian function or those who are due to undergo cancer treatment.
Sperm cells have been frozen and thawed successfully for more than 40 years. Depending on the quality of the initial sample, ejaculated sperm can be frozen for future use either in artificial insemination or in vitro fertilisation procedures.
Semen cryopreservation is often offered to males about to undergo cancer treatment in case the ability to produce viable sperm should diminish as a result of the treatment.
For couples undergoing fertility treatment, semen samples may be frozen prior to fertility treatment in case the male is not available, or may be unable to produce a sample on the day of treatment. Surgically retrieved sperm and testicular tissue (PESA/TESA) can also be frozen.
Donated sperm is routinely cryopreserved to maximise its utility and to allow quarantining of samples before use. Donors are screened for infectious diseases at the time of donation and again six months later. The cryopreserved samples are held until these results are available, at which point they can be cleared for use.
CAN OVARIES BE FROZEN?
Ovarian tissue can be cryopreserved, although the techniques are still in development and it is still considered by the IVF community to be an experimental method for fertility preservation. Approximately 30 babies have been born worldwide following cryopreservation of ovarian tissue.
When perfected, cryopreservation of ovarian tissue could be offered to patients requiring cancer treatment. It would offer a straightforward way of preserving many eggs without the need of ovarian stimulation, and could be an alternative or addition to freezing of embryos or eggs for sustaining fertility in women at risk of premature ovarian failure.
HOW LONG CAN GAMETES (SPERM / EGGS) OVARIAN TISSUE BE STORED?
As for embryos, sperm, eggs and ovarian tissue may be kept in storage for a period of up to five years, with an option to renew consent for a further five years.
For more information or queries regarding any of the services offered at Life Fertility Clinic, please contact us.