Sperm and
Embryo
Freezing

Key benefits




  • Sperm freezing and storage can performed as a back up to using fresh sperm, such as when a husband’s work commitments prevent him from being available to provide a fresh sample. It also a useful backup technique for husbands who may find it difficult to produce a sample on the day of egg pick-up.
  • After a stimulated ART cycle there may be surplus embryos. These can be cryopreserved and stored for use in a future cycle. This is embryo freezing.

Frozen Embryo Transfer (FET)

Many reproductive techniques result in the development of more embryos than can be safely transferred in one treatment cycle. It is possible to freeze embryos and to thaw them at a later date for transfer to the patient. This has a slightly lower pregnancy rate than fresh embryo transfers, but negates the need for a woman to go through a full treatment cycle to have another chance of achieving a pregnancy. The pregnancy rates with frozen embryos are nearly approaching those of fresh cycles. The embryos are transferred to the uterus without an anaesthetic in a hormonally controlled cycle. There has not been shown to be any increase in foetal abnormalities using frozen embryos. To be suitable for freezing, embryos must be growing at the expected rate and have few fragments between the cells of the embryos. If only one embryo is frozen from the original cycle, it is recommended that further IVF cycles are undertaken in order to have sufficient embryos for subsequent thawing and transfer.

If donor gametes are involved, embryos from different donors cannot be transferred together. It is important to be aware that approximately 75% of frozen embryos survive thawing in a condition which is suitable for transfer. This can be a very disappointing stage if you have had preparation for a frozen transfer cycle. The staff will be available to discuss this and support you and endeavor to provide the next step of your infertility care.

Long-term storage of frozen embryos is not recommended as a routine. The current Guidelines recommend that embryos not be stored for longer than five years other than in specific circumstances.

What are the specific steps in embryo freezing?


  • Embryos are removed from the 370C incubator and placed in a weak solution of CPA’s at room temperature. Embryos spend 8 minutes in this solution, which is enough time for the water and CPA’s to equilibrate. When first in the CPA solution, embryos initially shrink (as water leaves the embryo) and then re-expand as the CPA’s enter the cells.

  • Embryos are placed in a stronger CPA solution and allowed to equilibrate for just 1 minute.

  • Each embryo is loaded up into a fine straw which has been pre-labeled with identifying and tracking information. The label has information on the individual(s) that created the embryo (full names and date of birth), tracking information for any sperm and/or oocyte donor used, and the date of the freezing procedure and the status of the embryo at the time of freezing.

  • The straw is sealed at both ends and plunged into liquid nitrogen at a temperature of -1960C. It will remain at this deep sub-zero temperature until the individual(s) that created the embryo request for it to be warmed.

How are frozen embryos stored and monitored?

The air that we breathe contains a gas called nitrogen. This gas makes up about 78% of the air around us. If nitrogen gas is cooled, it becomes liquid at -1960C. This liquid is very stable and easy to work with. In the laboratory we have large tanks filled with liquid nitrogen in which we store frozen embryos. Each tank is in effect like a large thermos flask since it is vacuum lined. All patients have designated storage spaces within a tank, where their embryos are kept. The straws that contain the embryos are color-coded and labelled with precise and unique identifying information as described above.

The tanks that contain frozen embryos are monitored continuously. Each tank gets a physical inspection twice a day, looking for problems or signs of wear. The quantity of nitrogen in the tank is assessed as a means of monitoring for a possible slow leak or an impending tank failure. The nitrogen in the tank is topped up once or twice a week, since it continuously evaporates at a slow rate (if a tank was not filled regularly, the nitrogen would evaporate entirely in about 6 weeks).

How long can embryos be stored?

No one knows what the maximum storage period might be. Procedures for human embryo freezing were developed in 1984 and only went into widespread use in the late 1980s. This means that the longest time a human embryo has been stored is 25-30 years and, typically, patients that have left embryos in storage for this long are not coming back for them. Some patients have come back after 10-12 years and the embryos have been thawed successfully and created healthy babies. Beyond this time frame, we don't know how long an embryo will remain viable, but it is possible that, kept in liquid nitrogen, an embryo may be viable indefinitely.

How are embryos thawed?

The process of embryo freezing has already been explained. Thawing the embryos is simply a reversal of the freezing procedure.

When an embryologist removes embryos from the freezer, a second ............. person is required to witness the act, and verify the identity of the embryos before they can be thawed. Under no circumstances can a lone embryologist remove embryos from the freezer without another .................. person to confirm correct identification.

The embryos coming out of the freezer (at –196°C) are warmed to room temperature in 3 seconds. This rapid thaw method minimizes damage to the embryo from ice that could form during warming. The embryologist has to remove the antifreeze from the embryo and replace the water that was removed at the time of freezing. This is done by incubating the embryo in decreasing concentrations of the antifreeze, and increasing concentrations of water. Over a period of 20 minutes, the embryo is stepped through different solutions, until finally the antifreeze is gone and all the water has been replaced.

The thawing procedure is performed at room temperature, and once complete, the embryo is warmed up to body temperature (37°C). It can be ready for transfer in as little as 40 minutes after leaving the freezer.

Can freezing damage my embryos?

While every care is taken to protect the embryos during the process, some embryos may have one or more dead cells after they have been thawed. At Xenith, using the vitrificationmethos we have excellent survival rate after warming vitrified embryos. We consider a warmed (thawed) embryo as having a normal chance of implanting after transfer.

Am I more likely to have a child with a genetic or congenital abnormality because I'm pregnant after a frozen embryo transfer?

Even after 20 years, there are few studies in the scientific and medical literature concerning outcomes after embryo cryopreservation. However, the few studies that have been published are thus far very reassuring. Children born from frozen embryos do not seem different from children born from embryos that had not been frozen. Even if an embryo loses some cells during thawing this does not cause any abnormalities. Freezing does not cause or introduce genetic abnormalities.

What are my options for using the embryos?

We hope that most couples will be able to use the embryos to have a healthy baby. Patients undergoing frozen embryo transfer make up about one fourth of the patients visiting our office. Some are thawing embryos after failing to become pregnant during their IVF cycle, and some are using the embryos a year or more after a successful IVF cycle, to have a second or third child.

You may be surprised to learn that there are a significant number of people who do not want to use their frozen embryos to become pregnant. These are typically people that have completed their families and are not interested in having any more children. As per the current guidelines, all embryos in frozen storage for more than 5 years have to be destroyed if not claimed by the couple till then. Nonetheless, it is very important for all couples and individuals to think about what they might eventually do with excess embryos in the future should they find themselves in this situation. Some may want to freeze some eggs rather than fertilizing all eggs up front. Although a potentially costlier solution, it could help to avoid having to make an impossible choice at some future point.

Frozen embryos can also be donated for research studies. Embryos donated for research will be thawed and used in a scientific study, and discarded after a few days. A research study might look at new ways of freezing or thawing embryos, new ways of growing embryos in the laboratory or at the genetic make-up of the embryos. The studies will not benefit the patient that donates the embryos, but the research may benefit other IVF couples in the future.

How are embryos destroyed when patients request disposition?

A formal request to destroy the embryos must be received in writing from the patients. The request must be signed by both partners and notarized, or witnessed by a member of our staff. Once the laboratory has received the disposition notice, no action is taken for 30 days. This gives the couple a cooling off period and an opportunity to change their decision.

When the 30-day waiting period has passed, the Embryologist and the Clinical Doctor, take responsibility for carrying out the patients' wishes. They fill out a form indicating that they have checked the disposition request and are in agreement that the patient wants the embryos discarded. They locate the embryos in the storage tank and double check the identity with the paperwork. The embryos are then thawed and discarded. The paperwork is complete when both sign, attesting that they performed and witnessed the destruction according to the patients' wishes. The paperwork is kept in the laboratory files and a copy filed in the medical record of the patient.

Can I donate my embryos to another infertile couple?

Yes, it is possible to donate embryos. This process is referred to as embryo donation.

There are many advantages to embryo donation, including giving another couple the chance to have a child and avoiding having to discard the embryos that took so much effort to create. Couples wanting to donate surplus embryos can donate them anonymously to other couples through Xenith. Your Physician can explain the process to you. We always take consent from the couple before donating any surplus embryos and the embryos are donated or disposed only as per the wishes of the couple.

The couples donating and those receiving the embryos do not meet each other and only the consents are taken with complete counselling.

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