Frozen Embryos: The Process and Procedures

When couples (or people with ovaries) go though in vitro fertilization, many have additional embryos they choose to freeze to use for future attempts—either because the first cycle was unsuccessful or because they want to continue growing their family at a later date. 

This process involves freezing embryos to be able to complete a frozen embryo transfer (FET) at some point in the future. Embryo freezing is a procedure that allows people to store embryos for later use. (This differs from freezing eggs, which are not fertilized.) 

The main aim of freezing embryos is to preserve them for later use. Women or couples may opt to freeze their embryos for the same reason some women freeze their eggs—because they’d like to focus on their career, become more financially stable, or generally want to wait to add another person to their family. Using frozen embryos lets women have healthy pregnancies later in life; since the embryo contains younger eggs, there’s less risk of pregnancy complications. 

At Arizona Center for Reproductive Endocrinology & Infertility, we help patients through the entire multi-step process. Here’s a breakdown of the processes and procedures involved in freezing embryos. 


Retrieval and Fertilization 

The first few procedures for embryo freezing are identical to IVF. You will begin taking hormones for 8 to 10 days to ensure ovulation occurs. Then you’ll also take fertility medication to increase the number of mature, potentially fertile eggs that develop. 

Then, our doctor will extract the mature eggs, using an ultrasound machine to ensure accuracy. Since every patient is different, some women do suffer with more side effects than others depending on how many eggs are able to be retrieved. 

Once the eggs have been extracted from the ovaries, they’re fertilized in the lab. In order to become an embryo, the egg must be fertilized with sperm, either from a partner or a sperm donor.  

 At this stage, patients can opt for preimplantation genetic screening (PGS) to test embryos for genetic abnormalities, such as cystic fibrosis, muscular dystrophy, Huntington’s disease, and more. Along with genetic testing we can also do gender selection for additional costs.  

Dr. Gelety can then transfer the embryo to the uterus to complete the IVF process—this is known as a fresh embryo transfer. After the IVF cycle is completed, it is highly recommended for patients to freeze the extra embryos that were not transferred so that they do not have to go through the monitoring and retrieval process again. 


The Freezing Process 

 Embryos are frozen through a process called vitrification. The first step of this process is cryopreservation, which involves replacing the water in a cell with a substance called a cryoprotectant. This helps protect embryos from developing ice crystals, which can damage the embryo, during freezing.  

The cryoprotected embryos are then frozen extremely quickly. This helps protect the embryos and increases their rate of survival during thawing. After the process of freezing is complete, the embryos are stored in liquid nitrogen at temperatures of -321ºF. At this temperature, almost no biological processes, such as aging, can occur. So, in theory, a correctly frozen embryo can remain viable for any length of time. 


Thawing, FET, & Pregnancy 

 Typically, embryos can be thawed in an afternoon, and the process of thawing an embryo after cryopreservation has a relatively high success rate.  

When patients decide to thaw their frozen embryos and complete the FET cycle, there is less medication involved in the process—just what’s required to stimulate the woman’s uterine lining to prepare it for implantation. Then there’s usually only one to two ultrasound appointments to monitor the progress of her lining 

Before the FET, a catheter is loaded with the thawed embryos. Then, during the process, the catheter is placed in the uterus, using ultrasound guidance, and the embryos are transferred. The embryo transfer itself can be performed in under 30 minutes. 


Embryo freezing is a safe and successful option for patients who want to wait on having a baby. It often leads to a successful pregnancy and delivery. If you have specific questions regarding embryo freezing or would like to schedule an appointment to start the procedure, contact Arizona Center for Reproductive Endocrinology & Infertility today by calling (520) 326-0001 or visit us  online. 

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