Why would you consider freezing your embryos?

You may choose to freeze extra embryos and use them later if you:

• Postpone or cancel implantation into your uterus after an egg is already fertilized.
• Want to delay IVF to a later date.
• Want an option in case early attempts at fertility treatment fail.
• Choose to donate unused embryos to other people trying to get pregnant or to researchers rather than destroy them.

Embryo freezing is also used for fertility preservation. For example, a woman or person designated female at birth (DFAB) with cancer might want to save fertilized eggs before starting chemotherapy or radiation therapy if that treatment could affect their ability to get pregnant. A transgender man (transitioning to male) also might freeze eggs or embryos before taking hormones for the transition or having gender affirmation surgery.

How is the process perfomed?

The process is called vitrification, in which fertility professionals:

• Add a cryoprotective agent (CPA) to the embryos. CPA is a liquid that acts like antifreeze and protects cells from ice crystals.
• Place the embryos immediately into tanks of liquid nitrogen at -196.1° Celsius.

Who decides on embryo cryopreservation?

You have to give your permission to freeze embryos. Fertility specialist will give you consent forms to read and sign. The paperwork should provide details such as:

• How many embryos will be frozen.
• How long they’ll be stored.
• What happens when the storage time expires.
• What happens if you die or become too ill to make decisions before the storage period is over.
• What the embryos are allowed to be used for (for example, only your fertility treatments or if they can be donated to research or to another infertile couple).

Your fertility specialist can help you decide during which embryonic stage it’s best to freeze one or more embryos. The stages where freezing is possible include:

• Cleavage stage: When the single cell has multiplied to between four and eight cells after about 72 hours.
• Blastocyst stage: When the single cell has multiplied to between 200 to 300 cells after five to seven days.

 
Can you change your mind about freezing embryos?

You or your partner can change your mind at any time during the process. If one of the two parents decides not to proceed with the process, the fertility specialist can’t legally continue.

If one parent decides not to proceed after the embryos are already frozen, the specialist might suggest a waiting period to be sure. Then the embryos will be taken out of storage and allowed to perish.

 
What happens after embryo freezing?

When frozen embryos are needed later, a fertility specialist will:

• Remove the embryos from the liquid nitrogen.
• Allow them to slowly return to normal temperature.
• Soak them to remove the CPA.
• Use the embryos as indicated (for example, transfer them into your uterus).