According to the Committee Monitoring Assisted Reproductive Technologies (CMART), today there is an estimated 1 million In Vitro Fertilization (IVF) cycles every year around the world.

This makes IVF the most common fertility treatment pursued by infertile couples. But one of the least-talked about aspects of IVF is that many couples will end up with remaining embryos once their family building is complete.

When families have had as many children through the IVF process as they desire, they may have two, five, 10, or more embryos remaining in frozen storage at their clinic or in a cryo-bank. At some point they must determine what they will do (or not do) with these remaining embryos.

Today, there over 500,000 embryos frozen in storage in the U.S.

So, how exactly are embryos frozen? Here’s a quick look at some definitions that will help you understand the process:

Cryopreservation – the freezing of cells or tissue to preserve it for later use.

Time line – embryos are typically frozen at the blastocyst stage, or 5-7 days after their fertilization.

Vitrification – a commonly used, sped-up process of freezing tissues that involves adding a cryoprotectant to the water before freezing.

Cryoprotectant – a type of anti-freeze solution that helps to prevent ice crystals from forming in the water, which can be dangerous to frozen cells and tissue.

Freezing process – controlled freezing techniques slowly cool the embryos in the cryprotectant fluid. The fluid temperature gets as low as -196 degrees Celsius.

Straws – Long, plastic vials containing the embryos that are sealed prior to freezing. Usually there are no more than 1 to 3 embryos in each straw.

Dewars – Large, tank-like containers of liquid nitrogen which the straws are placed in.

To date, there has been no significant research showing an “expiration date” for frozen embryos. In fact, recently in the U.S. a healthy child was born from an embryo frozen for 20 years!

For more information about Embryo Donation, Adoption and storage, visit

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