Frozen embryo transfer
When embryos are frozen and transferred later, how your uterus is prepared, and what to know about the safety of frozen embryo transfer.
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In a frozen embryo transfer (FET), an embryo that was frozen during an earlier IVF cycle is thawed and placed in the uterus. It lets one egg retrieval support more than one chance at pregnancy.
When frozen embryo transfer is used
A frozen embryo transfer may be planned when:
- You choose preimplantation genetic testing (PGT) before transfer
- All embryos were frozen in the IVF cycle, with no fresh transfer
- Extra embryos remain after a fresh transfer that didn’t lead to pregnancy
- You’d like a second baby after a successful IVF cycle
When good-quality embryos won’t be transferred in the fresh cycle, they’re frozen for later use. Embryos are frozen with vitrification, a rapid freezing method associated with better embryo survival at thawing. Embryos can be stored for years.
Why freeze embryos
Freezing embryos can:
- Extend the potential of a fresh IVF cycle to later attempts, without repeating ovarian stimulation and egg retrieval
- Make it easier to transfer fewer embryos, including single embryo transfer
- Allow time for embryo testing with PGT
- Delay transfer when the uterine lining isn’t favorable in the fresh cycle, for example when it’s thin or has an unfavorable pattern
- Help some women with recurrent implantation failure or recurrent pregnancy loss, especially when embryos are tested first
Preparing your uterus
When you’re ready to use your embryos, we first check the uterine cavity with saline sonography (a simple office procedure) or hysteroscopy, and correct any abnormal findings. The uterine lining then needs to be prepared for transfer, in one of two ways.
Programmed cycle
A medication is given to pause your own egg development and estrogen production. Estrogen is then given until the lining of the uterus reaches a favorable thickness and pattern. This approach allows more flexibility in scheduling the thaw and transfer.
Natural cycle
Without added medication, we follow your follicle development up to ovulation with bloodwork and ultrasound. Embryos are thawed and transferred 3 to 6 days after ovulation, depending on the stage at which they were frozen. We prefer this approach for women who ovulate regularly.
Timing the thaw and transfer
Embryos must be thawed at the right time, so that the embryo’s age in days matches how far the uterine lining has developed. When timing is a concern after previous transfers, an endometrial receptivity analysis may help.
With vitrification, the large majority of embryos survive thawing.
Outcomes and safety
When a good-quality embryo was frozen, pregnancy rates after frozen embryo transfer are generally close to, and sometimes higher than, those with fresh embryos. Long-term follow-up of children born after frozen embryo transfer shows they are healthy, with no increase in birth defects or other disease.
To see how IVF outcomes are reported, visit our SART-reported success rates.
This article is general information, not medical advice. Every situation is different, so talk with your doctor about yours.
