Prior to the use of embryo cryopreservation, any remaining embryos following an embryo transfer or a canceled cycle (as in the case with hyperstimulation syndrome prior to embryo transfer) were discarded. With the development of improved cryopreservation techniques, these additional embryos can be frozen for use at a later time. Cryopreservation allows for subsequent "frozen embryo transfers" (FET) and additional attempts at conception. This helps to avoid additional stimulation of the ovaries with expensive fertility medications while saving the embryos for use in the future. This improves the overall safety and cost of infertility treatment. Oocyte recipients and IVF patients almost always choose cryopreservation as a means of extending their attempts at achieving pregnancy. The consent process for freezing eggs, sperm, and embryos must take into account several possibilites that could occur in the future before additional attempts at pregnancy are made. Examples of these events could include divorce or the death of one or both partners. Parent(s) must indicate their desires for disposition of the embryos in the event of a divorce or death of one of the partners. There are several options for extra embros created during IVF.
Freezing Embryos - Slow Freezing
Embryo freezing techniques have continued to evolve. The biggest challenge in freezing embryos is to protect them from damage during the freezing and thawing process. Ice crystals may form inside the embryo which can damage delicate structures inside of the embryo. The older technique of freezing embryos is referred to "slow freezing". During this procedure, a computerized device is used to control the slow decrease in temperature until the embryos reach the transition point between liquids and solids. A technique called seeding is used by touching the vial containing the embryos at the time when ice is forming within the liquid containing the embryos. This causes ice crystals to form in the container away from the embryos. To further prepare for this procedure, embryos are dehydrated and placed in cryoprotectants, or chemicals to protect the embryos from ice crystal formation. Embryos are usually frozen in groups of 1 to 2 per vial. This allows us to limit the number of embryos thawed at any given time in the future. We only thaw the number of embryos that are needed at the time of the frozen embryo transfer.
Freezing Embryos - Vitrification
The newest technique of freezing embryos is called vitrification. During this process, embryos are suspended in a thin membrane of liquid. Imagine a child's bubble wand with a thin layer of soap within the loop. Embryos are suspended in the cryo loop and plunged into liquid nitrogen. The thin layer of liquid and rapid nature of freezing will minimize the formation of ice crystals that can damage embryos. This technique has opened the doors to egg freezing and fertility preservation.
Survival of the embryos is not 100%, 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 3, day 5, and day 6). Once the embryos are frozen they do not have a known shelf life and do not deteriorate over time. Pregnancies have been reported from embryos stored over 16 years. The embryos chances of resulting in a pregnancy are based on the patients age when they are frozen and not when they are transferred. The survival of embryos after freezing is actually quite high. Poor quality eggs and poor quality embryos have a lower rate of survival, but in general, most embryos will survive the thawing process.
Another important concern is the safety of the techniques to the embryo and the potential future child. There have been many studies on the safety and long term effects of cryopreservation. Currently there is not any known risk associated with 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. The lab also uses a witness system and redundant paperwork to maintain strict protocols regarding identity and safety. [More Information]
Options for Frozen Embryos After IVF
When couples have left over embryos after IVF treatments, there are several options that are available. Patients are advised to keep the embryos until they are certain they no longer wish to keep the embryos. Often, several years after having a baby, patients may want another child even when they were certain they would not want additional pregnancies. Once the decision is made to no longer use the remaining frozen embryos, there are several alternatives to discarding the embryos. Embryos may be donated to research which may include procedures to improve laboratory techniques such as vitrification, donated to another couple, or transferred to the female at a time pregnancy is less likely to occur. Donating embryos to another couple gives the embryos a chance to make a pregnancy for a couple that may not have other means of becoming pregnant. Adoption programs are often very stringent and difficult when it comes to adopting a baby. Embryo Adoption offers couples a way to experience pregnancy because of the donating parents' gift of a new life.
Using donated embryos is not technically embryo adoption, though it's common to use these terms interchangeably. Most fertility centers prefer to use the term donor embryos or donated embryos as apposed to embryo adoption.