Freezing Embryos - Cryopreservation

When the term "test-tube babies" was first coined more than 25 years ago, eyebrows rose in skepticism. Today, creating life in a test tube is a common practice in treatments such as IVF, ICSI and Egg and Sperm donation. The will to procreate is very powerful and medical science has gone to great lengths to help couples in various stages of infertility to realize their dream of a baby.

Often assisted reproductive techniques (ART) like those mentioned above generate a number of embryos that exceed the number of those required for treatment. Depending upon the quality of the embryos, they can be frozen and placed in storage to be used at a future date.

Providing Enough Eggs to Create and Excess for Freezing Embryos

One of the phases of ART involves the stimulation of the ovaries in order to produce a larger number of eggs than would be produced under normal circumstances. Surplus embryos are created by fertilizing all of the eggs removed so there will be a selection of embryos to grow. This is done because not all embryos have the potential to grow. Only the best are chosen for replacement into the womb and about half of the time there are more quality embryos than the one or two necessary for replacement. These embryos are good enough to be able to survive the freezing process and still be viable when they are thawed. Storing these embryos allows for the possibility of another pregnancy (if the first failed) without having to go through the process of harvesting eggs and creating embryos again.

Advantages of Freezing Embryos

There are advantages to freezing embryos, called embryo cryopreservation:

· As mentioned above, the most important reason for freezing embryos is to have a surplus in the event more are needed at some point or to provide for another child.

· Ovarian hyperstimulation syndrome is a condition that can occur following ovarian stimulation for IVF. Women who are at risk for this condition are advised to freeze all embryos created in order to be sure there will be enough for transfer.

· Embryo cryopreservation is used when there is a risk of the implantation being compromised by endometrial problems (polyps, poor development), or breakthrough bleeding or illness.

· If there has been difficulty in the implantation of a fresh embryo because the cervix is narrow to scarred, then it is suggested that embryos be frozen to use in future efforts.

· Cryopreservation of embryos is an integral part of egg donation programs because it is not always possible to synchronize the cycle of the recipient with that of the donor.

· Successful pregnancies allow for excess frozen embryos to be made available for donation to infertile couples.

· When either of the partners is compromised with their health (cancer or other diseases) and requires potentially sterilizing treatments, embryo freezing is recommended and used.


Selecting Embryos for Freezing

Embryos are selected, placed into a cryoprotectant, which protects them from being killed in the freezing process, and then they are placed into a "straw" that is labeled with the particulars of the parents. This is done with a witness in order to ensure the details are correct. Then the straw is placed into a freezer and the temperature is lowered to -180C. From there, the straws go into a tank filled with nitrogen for storage.

The Process of Freezing Embryos

The embryos are stored at different stages of growth; one day (pronuclear stage, 2-3 days (4-8 cells stage) and 5-6 days (blastocyst stage). The earlier the embryos are frozen, the better the outcome seems to be when they are thawed. The statistics available indicate that about 70% of embryos survive this process without evidence of harm to normal development of a baby.

This process has a success rate, in most cases, of about 10-12% per thaw cycle. Some clinics spend more time nurturing early frozen embryos to the blastocyst stage in order to help with the potential of a pregnancy. Since several embryos are thawed at a time, this process can result in the loss of some while the nurturing process is carried out. However, the rate of successful pregnancies increases as a result of encouraging growth before implantation.

When the Frozen Embryos Aren't Needed

There are laws in place governing the disposition of embryos in the event of death, separation, or failure to instruct the facility storing the embryos. Usually, IVF facilities store frozen embryos for a period of five years and if they are not used within that period, then the individuals are required to determine how they want to proceed. They can sign again for another five years, donate the embryos or have them disposed of according to the standards of the clinic.

Once the embryo is thawed, it is transferred to the waiting mother. Read about frozen embryo transfer in our article in this section.

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