Frozen Embryo Transfer

By Angie Best-Boss

Babies on Ice. Snowbabies. Frozen embryos. Whatever you call them, freezing extra embryos for a later cycle may be the next step on your journey to family building. A FET, or frozen embryo treatment is when embryos frozen from a previous IVF cycle are thawed and placed in the womb. Fresh cycles almost always have an advantage over frozen cycles in most in vitro fertilization programs, but FET sometimes results in successful pregnancies.

Even Vegas singer Celine Dion has embryos sitting on ice. As she described it, "This frozen embryo that is in New York is my child waiting to be brought to life."

You might consider doing a frozen embryo transfer if you have undergone an IVF cycle and:

  • Were unable to transfer the embryos for any reason, such as ovarian hyperstimulation
  • You were successful and now want to expand your family
  • You were not successful and are ready to try again
  • You are using a donated embryo

How it works

The Reproductive Science Center of the Bay Area explains the process like this: "The embryo is loaded into a small straw, and placed in the cooling chamber of a controlled rate freezer. The embryo is cooled slowly to maximize water extraction from the embryo and to prevent the formation of large ice crystals that can damage the embryo. The entire process takes several hours and the frozen embryo(s) are stored in liquid nitrogen at –1960° C. Embryo thawing is a reversal of the freezing procedure. The embryos are removed from the storage tank and are warmed to room temperature in 30 seconds. For the next 30 minutes, the embryos are stepped through four different solutions until the cryoprotectant, the chemical used in the freezing solution to protect the eggs, is gone and all the water has been replaced. Thawed embryos are ready for transfer to the mother 40 minutes after their removal from storage."

Dr. Andrew Levi of the Park Avenue Fertility& Reproductive Medicine practice in Fairfield County, Connecticut says, "about 70-80% of high-quality embryos are expected to survive the thawing process. An embryo is said to survive if at least half of its cells are alive. For example, if a six-cell embryo is thawed, and three cells are alive, that embryo has survived the thaw. If the desired number of embryos does not survive the thawing process, additional embryos can be thawed in time for the scheduled embryo transfer since embryos thaw fairly rapidly."

The cost of an FET cycle is a fraction of the cost of a fresh IVF cycle and may be covered by insurance.

Easier Cycle

"This may not be true for everyone, but for me, I believe putting my body through the tremendous amount of stress that a retrieval can cause was a factor in an unsuccessful first attempt. For me, the second attempt using frozen embryos was much less physically and mentally stressful."

Frozen embryo replacement can be carried out in a cycle supported by HRT or in a "natural" cycle. If you use HRT, you need less medicine than in a traditional IVF cycle, but you still need to prepare your body for the transfer to ensure the most ideal conditions for implantation. You will also be given ultrasound scans to determine the best time to do the transfer. Plan on at least 40-50 days for a FET cycle.

Success rates

The biggest concern? How will the embryos do when thawed? Much of the success depends on the quality of the embryos at the time they were frozen. As a rule, around 30% of frozen embryos die when they are thawed out; however, around 30% of couples get a positive pregnancy test afterwards, and of those, up to 21% have a viable pregnancy.

Embryos may be frozen at any stage but only Grade 1 and 2 embryos are classed as suitable for freezing. Embryos are graded on a scale of 1-4 with 1 being the best. The quality of the embryos when frozen, the day on which they were frozen and the skill of the embryologist all play a role in whether or not a FET is successful. Ask your RE about their freezing/thawing success rates if you're concerned.

How many to transfer?

You will have to decide how many frozen embryos to transfer. Consider how you feel about multiples and if you are willing to do another cycle if needed. As Teri reports, "After 3 years trying to conceive with unexplained infertility, numerous IUI’s, Clomid, and 2 failed fresh IVF cycles, our first FET worked! We transferred 5 embies on day 3, and ended up with triplets!"


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