In Vitro Fertilization Process: Cryopreservation

If more embryos survive than are needed at the time of an embryo transfer, you may choose to have your embryos frozen, or cryopreserved, for later transfer.

Cryopreservation allows for subsequent frozen embryo transfers (FET) and additional attempts at conception without having to undergo additional stimulation with gonadotropins. This improves the overall safety and cost of infertility treatment.

Oocyte recipients and in vitro fertilization (IVF) patients very frequently choose cryopreservation as a means of extending their attempt at achieving pregnancy without the high-cost of a repeat IVF cycle, though the choice is optional.

The consent process for cryopreservation is separate from the IVF and donor cycle consents and should be completed (if desired) prior to the start of the cycle as the lab will need time to prepare the media for cryopreservation.

You may be advised to complete other IVF cycles prior to attempting FET.

Survival

Survival of the embryos is not 100 percent, but the techniques are designed to maximize the survival of the embryos.

Currently, embryos frozen at earlier stages tend to have a higher survival rate than embryos frozen at later stages (day two versus day six). The difficulty, however, lies in the fact that allowing the embryos to remain in culture longer improves the selection of embryos that are optimal for transfer. This results in a higher pregnancy per embryo transferred.

Many people ask if it is possible to freeze some embryos on day two and allow some to grow to day six. Unless there is a very large number of embryos this is not advisable because there is no way of determining which ones to culture and which ones to freeze.

Potentially the optimal embryos could end up frozen (thereby reducing their potential) while sub-optimal embryos are allowed to grow to day six.

While all things are considered on a case by case basis, the trend is to consider cryopreservation only after attempting an optimal transfer with fresh embryos.

Safety

Another important concern is the safety of the techniques to the embryo and the potential future child.

There is not any known risk associated with cryopreservation. There have been many studies on the safety and long-term effects of cryopreservation. Such studies are very difficult to conduct due to demographics of different countries, occurrence of abnormalities in the general population, and the number of years needed to make such assessments.

Our lab uses very strict techniques and labeling procedures to insure proper identification of embryos. In addition to indexed carriers, each holding "straw" (thin glass capillary tube) is labeled with a permanent marker. It is our utmost concern to prevent any errors in this aspect of the lab.

History

The first successful embryo cryopreservation was reported by Trounson and Mohr in 1983. Many techniques and protocols have been used since that time with the aim of improving the survival of the embryos undergoing cryopreservation.

One consistent step has been the slow freezing process combined with a rapid thaw. Other modifications have included the use of different media in which the embryos are frozen, as well as different cryoprotectants.

Ovarian Tissue Cryopreservation

A new area of exploration in the field of infertility is ovarian tissue cryopreservation.

This option offers patients undergoing surgical or medical treatments for other diseases, such as cancer, to preserve their ovarian tissue for later use. This technology may be offered to patients who will be delaying pregnancy for other reasons as well.

The ovarian tissue may be reimplanted for fertility purposes as well as hormone replacement in the case of a woman without ovarian function. This tissue is currently being preserved for use with the original "donor" and not for transplant into another woman.

More information will be forthcoming but if there are any questions you may have regarding ovarian preservation please contact our clinic at 919-572-HOPE (4673).