About 40 percent of patients who undergo IVF have an additional embryo(s) that they choose to cryopreserve (freeze) to use for another attempt, should their first cycle be unsuccessful, or to continue to build their family at a later date. This process is called a frozen embryo transfer (FET). But what goes into a frozen embryo transfer process, and what are the chances that those frozen embryos will result in a positive pregnancy test?
“For patients with a good prognosis who are 35 years old or younger, we can offer an approximately 60 percent pregnancy rate per embryo transfer,” says Dr. Anitha Nair of Shady Grove Fertility’s Washington, D.C. – K Street and Arlington, VA offices. “In turn, this means that the success rates for FET cycles are very similar as IVF cycles using fresh embryos.”
How Do You Freeze an Embryo?
Once a couple has gone through a fresh embryo transfer, any extra embryos that were not transferred and have made it to the blastocycst stage (day 5) are frozen via vitrification. This process is done by placing the embryo into a solution and then rapidly freezing it in liquid nitrogen. The rapid freeze increases the cooling rate and prevents the formation of ice crystals, which may cause breakage later. The most important part about this technique is the benefit of being able to thaw and transfer back fewer embryos compared to the “slow-freeze” process that was traditionally used, as the embryos frozen via vitrification have higher survival rates through the freeze and unfreeze process. Ultimately, this increases the chances of pregnancy for patients using frozen embryos.
“[Prior to vitrification] in order to optimize a patient's chances at pregnancy, we would transfer back one additional thawed embryo than we would transfer in a fresh IVF cycle,” explained Dr. Nair. “But with vitrification, we're more often transferring the same numbers of embryos, fresh or frozen with nearly the same pregnancy success rate.”
What to Expect During an FET Cycle
When the patient decides it's time to use the frozen embryo(s), the frozen embryo transfer process begins with a pre-medication ultrasound to ensure there are no cysts or other structural problems. Once cleared to start a cycle, you will take medication to optimize the lining of your uterus for implantation. You will give estrogen and progesterone injections every third day for up to 2 to 3 weeks, and your uterine lining is checked by post-medication ultrasound.
Dr. Nair explains that, although there are still medication protocols to follow, when a patient comes in for a FET cycle, there is typically significantly less medication, and patients find the process far easier and less stressful than undergoing a fresh IVF cycle.
“The whole frozen embryo transfer process is less intense and requires far fewer office visits,” explains Dr. Nair. “The patient will use less medication since all we're doing is stimulating her uterine lining to prepare for implantation. No ovulation medications are called for with an FET. Plus, there's usually only need for one ultrasound monitoring appointment to check her lining, as opposed to the frequent monitoring done with fresh cycles.”
After a couple weeks of preparation, it's time to thaw the frozen embryos and transfer them to the hopeful mother. Thawing takes very little time, just about an hour, so transfer day is eventful.
“We're conservative and start thawing only the number we intend to transfer,” Dr. Nair explains. “If those initial embryos don't come through the process in good shape, we'll thaw more if necessary. Generally, almost nine out of ten embryos survive the thawing process.”
Dr. Nair says that one of the interesting benefits of FET for many patients is that it's a little like freezing time. “Let's say a patient goes in for her IVF at the age of 33 and freezes some of the resulting embryos,” she said. “When she returns in a few years for an FET for her second baby, her ovaries and eggs will have aged and her fertility will have statistically decreased somewhat, but her frozen embryos are just as good cellularly as they were when she was younger. It's like a head start in the getting-pregnant process for older women.”
If you’re interested in learning more about the frozen embryo transfer process, please connect with your SGF medical team. To schedule a consult with a physician, please call 1-877-971-7755.
Editor’s note: This article was most recently updated in September 2016.