What Is a Frozen Embryo Transfer (FET)?

Key takeaways

• Frozen embryo transfer (FET) uses an embryo that was frozen earlier and later placed back into the body.
• IVF is the process that creates embryos in a lab; FET is a separate transfer step that can happen later.
• ART can use previously frozen embryos, and that is one reason a transfer may happen in a later cycle.
• When more than one embryo is transferred, the chance of a multiple pregnancy goes up.
• Transferring one embryo can lower the risk of twins or higher-order multiples MedlinePlus ASRM.

What is a frozen embryo transfer?

A frozen embryo transfer is the part of treatment where an embryo that was frozen earlier is thawed and placed into the parent’s body, usually the uterus. In assisted reproductive technology, embryos are created by removing eggs from the ovaries, mixing them with sperm, and then putting embryos back in the body; sometimes the embryos used are previously frozen ones MedlinePlus. That makes FET a transfer step within ART, not a description of the whole fertility treatment.

How is FET different from IVF?

IVF, or in vitro fertilization, is the process of combining an egg and sperm in a laboratory dish to facilitate fertilization. In the usual IVF cycle, eggs are collected, fertilized, and then embryos are monitored to see whether they develop. The embryo transfer may happen right away, or a frozen embryo can be used later in a separate cycle MedlinePlus ASRM.

That difference matters because people often use “IVF” as shorthand for the whole treatment path, but the transfer of a frozen embryo is its own step. IVF describes how the embryo is made. FET describes how a previously frozen embryo is transferred later.

Why would an embryo be frozen for later use?

Embryos may be frozen when there are extra embryos after an IVF cycle. ASRM notes that the recommendation for how many embryos to transfer is often based on age, history, and how many embryos are available to freeze, which is one reason freezing can be part of treatment planning ASRM. MedlinePlus also notes that ART procedures sometimes use previously frozen embryos MedlinePlus.

Freezing embryos can also support single-embryo transfer. When a clinic transfers one embryo and freezes other good-quality embryos for later, another transfer can happen in a future cycle instead of putting more than one embryo in at once ASRM.

Why do some people choose frozen embryo transfer instead of a fresh transfer?

A frozen embryo transfer can make sense when the best plan is to use an embryo in a later cycle rather than in the same cycle that created it. In ART, embryos may come from donor eggs, donor sperm, or previously frozen embryos, so treatment is not always a one-and-done process MedlinePlus.

One major reason clinics think carefully about transfer timing is the risk of multiple pregnancy. Transferring more than one embryo raises the chance of twins, triplets, or more. ASRM says the goal of elective single-embryo transfer is to decrease that risk, and MedlinePlus says multiple pregnancy is the most common complication of ART ASRM MedlinePlus.

What does embryo transfer planning have to do with multiple pregnancy?

The number of embryos transferred is a big part of the risk picture. MedlinePlus says multiple pregnancy can be prevented or minimized by limiting how many embryos are put into the parent’s body. ASRM likewise explains that transferring more than one embryo increases the chance of twins, triplets, or higher-order multiples MedlinePlus ASRM.

That is one reason FET is often discussed alongside elective single-embryo transfer. If one embryo is transferred now and another remains frozen, a later FET can use the stored embryo without increasing the embryo count in the uterus during the first transfer ASRM.

Who is usually considered for single-embryo transfer?

ASRM says women with the best prognosis for pregnancy are usually the ones considered for elective single-embryo transfer. Factors include being younger than 35, being in a first ART cycle, having had a successful prior ART pregnancy, having a relatively large number of high-quality embryos, and having embryos available for freezing to use later ASRM.

That does not mean every person needs the same transfer plan. It means the embryo transfer decision is tied to the larger treatment picture, including whether embryos are available to freeze and use in a later cycle.

What should you know about success and timing?

ASRM says freezing extra embryos and transferring them later can give a comparable pregnancy rate without the risks associated with twinning. The same source also notes that in good candidates, elective single-embryo transfer has shown excellent pregnancy rates, while overall pregnancy rates may be slightly lower in some groups because eSET is sometimes used in patients who are not ideal candidates ASRM.

It is also worth knowing that no method can reliably predict which embryo will produce a live offspring. Embryos are graded in the lab based on appearance, including cell number and size, rate of development, and other factors, but grading does not guarantee the outcome ASRM.

What are the main risks discussed with embryo transfer?

The biggest risk highlighted in the sources is multiple pregnancy. MedlinePlus says it is the most common complication of ART, and ASRM notes that transferring more than one embryo increases the chance of twins, triplets, or more MedlinePlus ASRM.

ASRM also notes that reducing a multifetal pregnancy later in pregnancy can carry risks, including the possibility of losing the entire pregnancy. That is part of why many patients and clinicians try to lower the chance of multiple pregnancy at the transfer stage rather than dealing with it later ASRM.

What is the simplest way to think about FET?

A helpful way to separate the terms is this: IVF makes the embryos, and frozen embryo transfer uses a previously frozen embryo in a later cycle. Both belong to assisted reproductive technology, and both are aimed at helping embryos be placed back into the body MedlinePlus.

For many people, that distinction is practical. It helps explain why one treatment cycle may create embryos, another cycle may transfer them, and the plan may include freezing embryos for later use. FET is not a different idea from fertility treatment; it is one distinct step within it.

Why does this distinction matter when you are planning treatment?

It matters because the transfer step affects how many embryos are used at once, whether a future cycle is possible, and how much attention is paid to the risk of twins or more. MedlinePlus and ASRM both frame ART around a sequence: eggs are removed, fertilized, embryos are formed, and embryos are returned to the body, sometimes after freezing MedlinePlus ASRM.

When you know FET is a later transfer step rather than the whole IVF process, it is easier to understand the treatment timeline and the choices that come with embryo storage and embryo number.