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Cryopreservation of Embryos

Why freeze your embryos?

An embryo is created when an egg is fertilized by a sperm in the lab. Like eggs and sperm individually, embryos can be frozen for use with ART in the future. Embryos are often frozen because more than one is created during a course of treatment, such as in vitro fertilization (IVF).

IVF has a better chance of success when more than one ovarian follicle and more than one egg develop during the treatment cycle. All available eggs are retrieved from your ovaries, and the best eggs are chosen for insemination in the lab.

The pregnancy rates following embryo transfer in an IVF cycle are directly related to the number and quality of embryos transferred. However, transfer of an excessive number of embryos significantly increases the chance of a multiple pregnancy (twins, triplets, etc.) and the associated obstetrical risks. Therefore, the number of embryos transferred must be limited, potentially leaving eggs or embryos left over.

There are two options for remaining eggs that are not used to create embryos for transfer — they may either be discarded without fertilization or inseminated and cryopreserved as embryos for later use.

Insemination of all extra eggs and cryopreservation of any resulting embryos offers several advantages:

  1. Cryopreserved embryos may be transferred during subsequent months without the need for additional surgery, thereby increasing the chances of conceiving as a result of any one surgical procedure.
  2. Cryopreserved embryos may be transferred in cycles during which minimal or no medication is used.
  3. Because embryos are more substantial, they may withstand the freezing process better than eggs.

What is the process for freezing embryos?

The process for freezing embryos is very similar to freezing eggs, with the added step of joining the eggs with sperm, either from your partner or a donor, in the lab.

Embryos can be successfully frozen at several different developmental stages. The decision as to the optimal timing for freezing varies by lab and procedure. The following are Midwest Fertility’s guidelines:

  1. On the first day after egg retrieval, the eggs will be evaluated for signs of fertilization and for overall appearance.
  2. On day three, the embryos will again be evaluated by the lab. If your embryos are progressing according to the biologist’s criteria, they will continue to monitor your embryos through to the blastocyst stage (day five).
  3. If you are going through treatment, on day five, the highest quality embryos will be transferred, and any others that are still progressing will be cryopreserved on either day five or six.

We will keep you informed as to the status of your embryos.