Overview
A frozen embryo transfer (FET) uses an embryo created in an earlier IVF or ICSI cycle and frozen, rather than one transferred fresh a few days after egg collection. The embryo is thawed on the day of transfer and placed in the womb through a thin catheter, in a cycle where the womb lining has been prepared to receive it.
Frozen transfers have become a routine part of IVF. Spare good-quality embryos from a fresh cycle can be frozen and used later without repeating stimulation and egg collection. Some clinics freeze all embryos and transfer none fresh, for example when there is a high risk of ovarian hyperstimulation syndrome (OHSS) or when embryos are being genetically tested. The HFEA says most embryos survive thawing, and that success rates with frozen embryos are comparable to fresh ones.
Freezing every embryo as a routine policy (an elective freeze-all) is more debated. The HFEA rates it amber for increasing the chance of a baby, because studies conflict, and green for reducing the risk of OHSS. It also notes that babies from frozen transfers tend to have higher birth weights and that there is a higher risk of pre-eclampsia, so caution is needed before applying freeze-all to everyone. ESHRE's 2023 recommendations do not recommend elective freeze-all for routine use.
Who it's for
- People with spare frozen embryos from an earlier cycle who want to try again without another egg collection.
- People whose fresh transfer was cancelled, for example because of a high risk of OHSS.
- People whose embryos have had preimplantation genetic testing and were frozen while waiting for results.
- People travelling for treatment who prefer to split the cycle into two trips: one for egg collection and one for transfer.
Whether a treatment suits you depends on your own history and tests — discuss it with a fertility specialist.
Step by step
Planning the cycle
The clinic decides with you whether to use a natural cycle or a medicated one. A natural cycle relies on your own ovulation and suits people with regular periods; a medicated cycle uses hormones to prepare the lining and suits people with irregular or absent periods, or those who need a fixed date.
Preparing the womb lining
In a medicated cycle, oestrogen tablets or patches thicken the lining over around two weeks, sometimes after medication to pause the natural cycle. In a natural cycle, scans and blood or urine tests track ovulation.
Monitoring
One or more ultrasound scans check the thickness and appearance of the lining, and blood tests may check hormone levels. The transfer date is set once the lining is ready.
Progesterone
Progesterone, given as pessaries, gel or injections, prepares the lining to receive the embryo. The timing of transfer depends on the embryo's stage when it was frozen.
Thawing
On the day, the embryo is thawed in the laboratory. The clinic checks it has survived; occasionally an embryo loses a few cells or does not survive, in which case another may be thawed if available.
Embryo transfer
The embryo is placed in the womb through a thin catheter, usually guided by an abdominal ultrasound. It takes a few minutes and normally needs no sedation.
Pregnancy test
Hormone support usually continues until the pregnancy test, about two weeks later, and for some weeks into a pregnancy if the test is positive.
Typical timeline
- Consultation and planning
- Usually in the cycle before transfer
- Lining preparation (medicated or natural)
- About 2–3 weeks from the start of the period
- Progesterone before transfer
- About 3–6 days, depending on the embryo's stage
- Transfer to pregnancy test
- About 2 weeks
- Whole cycle
- Typically 3–5 weeks; the time you must be present at the clinic is often much shorter
What it costs
A frozen transfer is usually much cheaper than a new stimulation cycle, but the price varies with the medication and monitoring needed. Superior A.R.T. publishes an estimate of 60,000–70,000 baht per frozen transfer cycle, plus about 15,000 baht for preparation medication. Also check the annual storage fee for remaining embryos, and whether a package price includes a frozen transfer or only a fresh one.
Risks and side effects
- Not every embryo survives thawing, and very occasionally none do.
- Multiple pregnancy if more than one embryo is transferred. The HFEA says one embryo is usually transferred, and single embryo transfer reduces this risk.
- The HFEA notes that babies from frozen transfers tend to have higher birth weights, with a higher risk of large-for-gestational-age babies and of high blood pressure disorders in pregnancy such as pre-eclampsia.
- Side effects of hormone medication, such as bloating, breast tenderness or mood changes, in medicated cycles.
- Ectopic pregnancy and miscarriage remain possible, as with any IVF pregnancy.
Questions to ask a clinic
- Do you recommend a natural or a medicated cycle for me, and why?
- Which parts of the preparation can be monitored at a clinic near my home?
- What is your laboratory's survival rate for thawed embryos?
- How many embryos would you transfer, and what is your single embryo transfer policy?
- What does a frozen transfer cost, including medication, and is it included in my package?
- If you recommend freezing all embryos, why, and what is the evidence for my situation?
- What does storage cost for my remaining embryos, and how do I renew it?
Frequently asked questions
Are frozen embryo transfers as successful as fresh ones?
The HFEA says success rates with frozen embryos are comparable to fresh embryos and have risen year on year. Results still depend mainly on the age at which the eggs were collected and the quality of the embryo.
Is a natural or medicated cycle better?
Studies comparing them have produced mixed results. A natural cycle avoids most medication but needs flexible timing; a medicated cycle allows the transfer date to be planned. Your specialist will suggest an approach based on your cycle and history.
How long can embryos stay frozen?
The HFEA says there is no evidence that the length of freezing affects embryos, though long-term effects cannot be ruled out. Storage limits are set by law and by the clinic's storage agreement.
Should I freeze all my embryos and transfer later?
Freezing all embryos is well supported for reducing OHSS risk, but the evidence that it improves the chance of a baby for most patients is conflicting. Ask your clinic why it is recommending it for you.
How long do I need to be in Thailand for a frozen transfer?
Often much less than for a full IVF cycle, because early preparation can sometimes be monitored at home. Ask the clinic how many days before transfer you need to arrive and how soon after you can fly.
