Frozen Embryo Transfer (FET): What to Expect & How to Prepare

Frozen Embryo Transfer (FET): What to Expect & How to Prepare

Quick answer: A frozen embryo transfer (FET) is a procedure where a previously frozen embryo is thawed and placed into the uterus. It’s a short, catheter-based procedure that needs no sedation and takes a few minutes. The work is in the weeks beforehand: preparing the uterine lining, either in a natural cycle (using your own ovulation) or a medicated cycle (using oestrogen and progesterone). Success depends far more on embryo quality, uterine health, and age than on which protocol you use.

Frozen embryo transfer sounds more complicated than it is. The transfer itself is quick and gentle; most people are surprised by how undramatic it feels. The part that takes planning is preparing your body to receive the embryo at exactly the right moment.

This guide walks through the whole process: how the lining is prepared, the difference between natural and medicated cycles, the day of transfer itself, the two-week wait, and what the success data actually shows. It also explains why FET has become so common that, in the UK, frozen transfers now often outnumber fresh ones.

What is a frozen embryo transfer?

A frozen embryo transfer is the use of an embryo that was created in an earlier IVF cycle, frozen, and stored, then thawed and transferred when the time is right. Embryos are frozen using vitrification, a flash-freezing technique that prevents ice-crystal damage and gives survival rates on thawing of around 90-95%.

FET is used in several situations: after a fresh IVF cycle produced more than one good embryo, when embryos were frozen to allow genetic testing (PGT-A), when the body needs time to recover after stimulation before transfer, or when a first transfer wasn’t successful and there are embryos in storage to try again.

Freezing embryos and transferring them later isn’t a compromise. For many patients it’s the deliberate, better-planned route: the lining can be prepared calmly, without the hormonal intensity of a fresh stimulation cycle happening at the same time.

Natural vs medicated FET: the two main approaches

The central decision in an FET is how to prepare the endometrium: the uterine lining the embryo implants into. There are two routes.

Natural cycle FET works with your own ovulation. Your cycle is tracked with scans and blood tests to pinpoint ovulation, and the transfer is timed to your body’s natural window. It uses little or no hormone medication. It suits women with regular, predictable cycles.

Medicated (hormone-replacement) FET uses oestrogen to build the lining and progesterone to prepare it for implantation, with the transfer timed by the medication rather than your own cycle. It gives more control over scheduling and suits women with irregular cycles or those who don’t ovulate predictably.

Neither is dramatically superior for everyone. Both achieve broadly comparable pregnancy rates, and the right choice depends on your cycle, your history, and practical factors your doctor will talk through.

The FET timeline, step by step

The exact days vary with your protocol and your body, but the sequence is consistent.

Preparation (roughly 2-4 weeks before transfer). In a medicated cycle, oestrogen starts near the beginning of your cycle to build the lining. In a natural cycle, monitoring begins to track ovulation. Either way, scans confirm that the endometrium is nicely developed, measuring 7-8mm or more, with good endometrial quality, confirming it’s suitable for proceeding with the transfer.

Starting progesterone. Once the lining is ready, progesterone begins. This is the hormone that makes the lining receptive and sets the precise timing of transfer. The number of days on progesterone before transfer depends on the embryo’s stage (a day-5 blastocyst is transferred after five days of progesterone).

Thawing the embryo. On the day of transfer, the embryologist thaws the chosen embryo and confirms it has survived and looks healthy before proceeding.

The transfer. A fine, soft catheter is passed through the cervix under ultrasound guidance, and the embryo is placed into the uterus. It takes a few minutes, needs no sedation, and feels similar to a smear test. You can usually get up and carry on with your day shortly afterwards.

The two-week wait. Progesterone (and sometimes oestrogen) continues to support the lining. A blood test around 10-14 days later measures hCG to confirm whether implantation has occurred.

Bed rest afterwards isn’t necessary; the evidence doesn’t support it. A gentle walk after the transfer is always recommended and perfectly fine, and normal, everyday activity is fine too. Your clinic will tell you what to continue and what to pause.

Fresh vs frozen transfer: which is better?

For years, fresh transfers were the default. That’s changed as freezing techniques improved, and frozen transfers are now extremely common. In some UK data, FET live birth rates match or exceed fresh transfers, partly because the body isn’t recovering from stimulation at the same time, giving the lining a calmer environment.

That said, it isn’t universal. For some patients a fresh transfer is the better choice. The decision depends on how you responded to stimulation, your hormone levels, whether genetic testing is planned, and your individual history. It’s a clinical judgement made with your doctor, not a fixed rule.

How to prepare for your FET

Most of what helps is straightforward:

Take medications exactly as scheduled; timing is the whole point of the protocol, especially progesterone. Keep monitoring appointments so lining thickness and timing can be confirmed. Continue any recommended supplements (folic acid is standard pre-pregnancy). Eat and sleep normally; there’s no special diet that changes implantation. Keep alcohol out and moderate caffeine, as you would in early pregnancy. Ask your clinic before starting or stopping anything.

The single most useful thing is a clear medication calendar: what to take, when, and for how long. It removes most of the stress from the practical side.

Frequently asked questions

Is a frozen embryo transfer painful? For most people, no. The transfer is a quick, catheter-based procedure done without sedation, similar to a cervical smear. Some mild cramping afterwards is normal.

What is the success rate of FET? It depends mainly on embryo quality, your age at the time the embryo was created, and uterine health. UK figures put live birth rates per frozen transfer broadly in the region of 30% or higher, and often comparable to or better than fresh transfers. Your doctor can give a realistic figure for your specific situation.

Natural or medicated FET, which is better? Both achieve broadly similar pregnancy rates. Natural cycles suit regular, predictable cycles; medicated cycles suit irregular cycles and offer more scheduling control. The right choice is individual.

How long does the FET process take? Preparation usually spans two to four weeks, depending on the protocol, followed by the transfer and a two-week wait before a pregnancy blood test.

Do frozen embryos survive thawing? Modern vitrification gives survival rates of around 90-95%. The embryologist confirms the embryo has thawed well before the transfer goes ahead.

Do I need bed rest after the transfer? No. The evidence doesn’t support bed rest. A gentle walk is always recommended and perfectly fine, and normal, everyday activity is fine too. Your clinic will advise on anything to pause.

Key takeaways

• FET thaws a stored embryo and transfers it in a short, sedation-free procedure.
• The preparation, building and timing the uterine lining, is where the work happens.
• Natural cycles use your own ovulation; medicated cycles use oestrogen and progesterone. Both work well.
• Success depends mostly on embryo quality, age at freezing, and uterine health, not the protocol.
• Vitrified embryos survive thawing around 90-95% of the time; a gentle walk afterwards is fine, and bed rest isn’t needed.

A frozen transfer is one of the more manageable steps in fertility treatment. With the lining prepared and the timing right, the transfer itself is quick, and the planning is entirely doable.