What a Frozen Embryo Transfer Cycle Looks Like

What is a frozen embryo transfer?

A frozen embryo transfer is the second half of an IVF cycle that was split in two: eggs were retrieved and fertilized earlier, the embryos were frozen, and now one is thawed and placed in the uterus. Because clinics almost always transfer a single embryo to avoid the higher risks that come with twins, most people go into an FET planning to move just one embryo 1Ref 1Practice Committees of ASRM and SART (2021).Guidance on the limits to the number of embryos to transfer: a committee opinion.That a single embryo is usually thawed and transferred in an FET, because elective single-embryo transfer preserves pregnancy rates while lowering multiple-gestation risk.2Ref 2Practice Committee of ASRM and SART (2022).Multiple gestation associated with infertility therapy: a committee opinion.That multiple gestation is the main avoidable risk of infertility therapy, the reason clinics transfer one embryo at a time..

FET — a frozen embryo transfer, in which a thawed, previously frozen embryo is placed during a later cycle.

There is no ovarian stimulation and no egg retrieval this cycle, which makes an FET physically gentler than the retrieval half of IVF. If more embryos remain frozen, the same steps can be repeated later from the same batch.

Step 1 — Planning the cycle and choosing a protocol

The cycle starts with a planning visit and a baseline check, usually an ultrasound and bloodwork early in a menstrual cycle to confirm the ovaries and lining are quiet and ready to begin. At this visit you and the clinic settle on the protocol. A medicated FET uses hormones to build and time the lining; a natural FET tracks your own ovulation instead.

The medicated vs natural frozen embryo transfer choice shapes the whole calendar that follows — how many monitoring visits you have, and whether the transfer date is set by medication or by your body's own timing. Which fits depends on your cycles and your clinic's preference, and it is worth discussing directly rather than assuming one is standard.

Step 2 — Preparing and monitoring the uterine lining

For a week or two the focus is the endometrium, the lining the embryo will implant into. In a medicated cycle, estrogen is given to thicken it; in a natural cycle, the clinic tracks the lining as your own body prepares it. Either way, you return for a few ultrasound scans and blood tests.

The transfer is scheduled by how the lining looks and behaves, not by a fixed date on the calendar.

The team is watching for the lining to reach a receptive thickness and pattern. If it is not ready, the clinic may extend the medications or, occasionally, pause and try again next cycle. That is a common adjustment, not a failure.

Step 3 — Timing the transfer to the implantation window

The transfer is timed to a short window when the lining is briefly receptive. Once the lining looks right, progesterone is started, and that start date opens the window. The transfer is then booked a set number of days later, matched to whether the embryo was frozen at the cleavage stage or as a blastocyst, so the embryo's developmental age lines up with the lining.

Some clinics offer extra tests or add-ons meant to fine-tune this timing, such as an endometrial receptivity test or an endometrial scratch. The UK regulator that rates IVF add-ons finds that many of them have limited evidence of benefit, so they are worth asking pointed questions about — and pricing carefully — before agreeing to them 3Ref 3Human Fertilisation and Embryology Authority (2024).Treatment add-ons with limited evidence.That the UK regulator rates many IVF add-ons — including endometrial receptivity testing and the endometrial scratch — as having limited evidence of benefit..

Step 4 — Thawing the embryo and the transfer itself

On transfer day the embryologist thaws the chosen embryo, and most survive the warming well. The transfer itself is quick and usually painless: a speculum is placed, and a thin, soft catheter carries the embryo through the cervix into the uterus under ultrasound guidance. It generally takes a few minutes, needs no anesthesia, and you can get up soon afterward. Usually a single embryo is thawed and transferred 1Ref 1Practice Committees of ASRM and SART (2021).Guidance on the limits to the number of embryos to transfer: a committee opinion.That a single embryo is usually thawed and transferred in an FET, because elective single-embryo transfer preserves pregnancy rates while lowering multiple-gestation risk..

If the embryos were genetically tested, a chromosomally normal embryo is often chosen to go first. Testing can help with selection, but large trials have not shown that it raises live-birth rates for most patients, so whether it helps in your particular case is a fair question to put to your clinic 4Ref 4Practice Committees of ASRM and SART (2024).The use of preimplantation genetic testing for aneuploidy: a committee opinion.That PGT-A has not been shown to improve overall live-birth rates for the general IVF population, so its benefit in an individual case is uncertain..

Step 5 — Progesterone support and the two-week wait

After the transfer, progesterone support continues to keep the lining ready, and then comes the part most people find hardest: the wait. A blood test for the pregnancy hormone hCG — the beta test — is scheduled roughly nine to fourteen days later, and it is more reliable than an early home urine test.

Light cramping, bloating, or a little spotting in this window is common and does not, by itself, mean the cycle has failed.

Home tests can read falsely positive if trigger medication is still in your system, or falsely negative if taken too soon, which is why clinics rely on the timed blood test rather than a stick at home.

What are the odds, and what if it doesn't work?

The chance that one transfer leads to a live birth depends heavily on age and on the embryo, and US national data reported by clinics break this out by the patient's age band rather than offering a single number 5Ref 5Society for Assisted Reproductive Technology (SART) (2024).National Summary Report (SART CORS Online).US national IVF outcomes reported by SART member clinics, broken out by patient age band, used here for per-transfer live-birth context rather than any single clinic's claim.. There is no honest way to promise an outcome from one transfer.

A transfer that does not work is common and does not mean the next one will fail. IVF success tends to accrue over more than one attempt, so cumulative odds across several transfers are higher than any single try — though they still decline with age 6Ref 6Smith ADAC, Tilling K, Nelson SM, Lawlor DA (2015).Live-Birth Rate Associated With Repeat In Vitro Fertilization Treatment Cycles.That IVF live-birth rates accrue over repeated cycles, with cumulative odds higher than any single attempt but still declining with age.. If you are weighing what an FET cycle costs against those odds, or comparing the frozen embryo transfer vs. fresh transfer question, those are worth mapping out before you start.