Frozen Embryo Transfer (FET)

Medically reviewed by Dr Manjushree Boob, MD, DNB, FICMCH, FICOG - Infertility & IVF Consultant

What it is

Frozen embryo transfer (FET) is the second half of an IVF cycle, done separately. In the first half, eggs are collected, fertilised in the laboratory, and grown for a few days. Instead of being placed into the uterus straight away, the resulting embryos are frozen and stored. In a later cycle, when the uterine lining has been prepared, one embryo is thawed and placed into the uterus.

The freezing method matters. Older slow-freezing techniques allowed ice crystals to form inside the cell, which damaged embryos. Vitrification, which is what is used now, cools the embryo so rapidly that the fluid inside turns glassy rather than crystalline. Survival rates after thawing are high, and the embryo that goes back is essentially the embryo that was frozen.

What began as a way of storing spare embryos has become, for many couples, the preferred way to transfer them at all.

Who needs it

• Anyone with good embryos left over after a fresh transfer - these are stored for a second attempt without repeating egg collection.
• Women at risk of ovarian hyperstimulation syndrome (OHSS), where transferring in the same cycle would make a swollen, uncomfortable situation genuinely dangerous. Freezing everything and transferring later removes that risk almost entirely.
• A raised progesterone level on the trigger day, which shifts the lining out of step with the embryo and lowers the chance of a fresh transfer working.
• A thin or poorly prepared endometrium in the stimulation cycle, which we can do better in a controlled cycle.
• Couples doing genetic testing on embryos (PGT), where the results take days or weeks and a fresh transfer is impossible.
• Fertility preservation - embryos frozen before cancer treatment, or before surgery that may affect ovarian reserve.
• Anything that makes this month the wrong month - an infection, a polyp found on scan, a fibroid needing attention, travel, illness, or simply a couple who need a pause.

“Does freezing harm the embryo? It feels like an unnatural thing to do to it.” I understand why it feels that way. But the embryo is not asleep and waiting - at minus 196 degrees nothing at all is happening to it, no ageing, no metabolism, no damage accumulating. The only moments of risk are the freeze and the thaw, and vitrification has made both remarkably safe. The embryo we put back is the same one we froze.

How it is done

An FET cycle is mostly about the uterus. The embryo already exists; the job is to get the lining ready to receive it.

Choosing the cycle type. There are two broad routes. In a hormone replacement (medicated) cycle, oestrogen tablets or patches are started early in the cycle to build the lining, and the timing is entirely in our hands. In a natural or modified natural cycle, we track your own ovulation with scans and transfer at the point your body dictates. Which suits you depends on how regular your periods are, your previous cycles and your own preference.

Preparing the lining. Oestrogen is given for roughly ten to fourteen days. Scans check the thickness and pattern of the endometrium. When it reaches a satisfactory thickness with the right appearance, progesterone is added - vaginal pessaries or gel, sometimes injections - and this is what sets the transfer date.

Timing the thaw. The number of days of progesterone before transfer matches the age of the embryo when it was frozen. A blastocyst frozen on day 5 goes back after five full days of progesterone. This synchrony matters more than almost anything else in the cycle.

Thawing. On the morning of the transfer the embryologist warms the embryo, checks that it has survived and is re-expanding, and grades it. You will be told before you go into the room how it looks.

The transfer itself. You lie as you would for an internal examination, with a comfortably full bladder so that the ultrasound picture is clear. A speculum is passed, the cervix is gently cleaned, and a soft, fine catheter is guided through the cervix into the uterine cavity under abdominal ultrasound guidance. The embryo, in a tiny drop of fluid, is released at a chosen point in the cavity. The catheter is withdrawn and handed to the embryologist, who checks under the microscope that it is empty.

Afterwards. You rest for a short while, empty your bladder - yes, it is safe - and go home.

Anaesthesia, duration and hospital stay

No anaesthesia is needed for a standard transfer. It is not a surgical procedure; most women compare it to a smear test or a slightly uncomfortable internal examination. Occasionally, where the cervix is difficult to negotiate, we use light sedation, and we will discuss that beforehand.

The transfer takes about five to ten minutes. You will be in the unit for an hour or two in total, most of it waiting and resting.

There is no hospital admission and no stay. You come in the morning and go home the same day.

Recovery

The same day. You can eat normally, travel home, and sleep in your own bed. Some women have mild cramping or a small amount of spotting from the cervix - both are common and mean nothing about the outcome.

The first week. Continue every medicine exactly as prescribed, particularly the progesterone. Do not stop it because you feel a symptom or because you do not. Walk, work, cook, drive. Avoid heavy lifting, high-impact exercise, hot tubs and intercourse.

The two-week wait. This is the hardest part of the whole treatment and there is no medical trick that shortens it. Symptoms are useless as a guide - progesterone produces sore breasts, tiredness, mild cramps and nausea whether or not you are pregnant. Cramping does not mean failure and its absence does not mean success.

The test. A blood beta-hCG on the day we tell you. If it is positive, the progesterone continues and a scan is arranged at around six to seven weeks to confirm the heartbeat. If it is negative, we stop the medicines, let a period come, and sit down together to look properly at what to change - not immediately, but when you are ready.

Contact us sooner for heavy bleeding, severe pain, fever, or a rapidly swelling abdomen.

Why a frozen transfer rather than a fresh one

For years, a fresh transfer was the default and freezing was for leftovers. That has changed, and here is the reasoning patients usually want to hear.

• The hormonal environment is normal. Stimulation produces oestrogen levels many times higher than a natural cycle, which can make the lining less receptive. An FET cycle does not have that problem.
• OHSS risk essentially disappears. In a woman with a high response, a pregnancy in the same cycle can turn moderate hyperstimulation into a serious illness. Freezing all embryos avoids this.
• The lining can be prepared properly, with time to fix a thin endometrium, treat a polyp, or simply try again next month if it is not right.
• Timing becomes flexible. Transfer when you are well, when you are not travelling, when the results of genetic testing are back.
• Better obstetric outcomes in some studies - lower rates of low birth weight and preterm delivery compared with fresh transfers, though the data are not uniform and are still being studied.

A fresh transfer is still the right choice in some situations - a modest number of eggs, no OHSS risk, an ideal lining and a couple who would rather not wait. It is a decision made case by case, not a rule.

Risks and complications

FET is one of the safest steps in fertility treatment, but it is honest to state what can happen.

• The embryo may not survive the thaw. Uncommon with vitrification, but not impossible. Where there is more than one embryo stored, another can be thawed the same day.
• A difficult transfer, where the cervix is narrow or angled, occasionally needing a different catheter or a small dilatation.
• Cramping and spotting, usually minor and short-lived.
• The cycle may be cancelled before transfer if the lining does not respond, if ovulation happens too early in a natural cycle, or if a fluid collection or polyp appears. Frustrating, but better than transferring an embryo into an unfavourable uterus.
• Failure to implant. The commonest disappointment in all of IVF, and often for reasons we cannot identify in a single cycle.
• Miscarriage, at broadly the same rate as in a natural conception at your age.
• Ectopic pregnancy - uncommon, but possible even though the embryo is placed inside the uterus, which is why an early scan matters.
• Multiple pregnancy if more than one embryo is transferred, with all the risks that carries for mother and babies.
• Side effects of the medicines - bloating, headache, mood changes, breast tenderness, and vaginal irritation from pessaries.

Alternatives

A fresh embryo transfer in the stimulation cycle, where circumstances are favourable.

A natural-cycle FET instead of a medicated one, for women with regular ovulation who would rather use fewer hormones.

Another egg collection cycle, if no embryos are stored or the stored ones are of poor quality.

IUI or timed intercourse cycles, appropriate for some couples with mild factors who have not yet needed IVF at all.

Donor eggs, donor sperm or a donor embryo, where the underlying problem cannot be solved with your own gametes.

Pausing treatment. Not a failure and not a defeat. Fertility treatment is physically and emotionally expensive, and there is nothing wrong with taking a break before the next attempt. If you want to understand where FET sits in the wider picture, our IVF and fertility treatments page covers the full pathway, the ICSI page explains how the embryos are created in the first place, and you can see all the procedures we perform.

What it costs

There is no single published figure for FET at our centre, because what you pay depends heavily on which parts of the pathway you need. Rather than quote a number that may not apply to you, here is what actually drives the cost:

• The cycle protocol - a medicated cycle uses more medication than a natural-cycle transfer.
• The medicines themselves, which vary widely in brand and dose.
• The number of monitoring scans and blood tests your cycle needs.
• Embryo storage charges, usually billed for a defined period.
• The thaw and laboratory work on the day.
• Whether genetic testing (PGT) was done on the embryos, which is a separate and significant cost.
• Any additional procedure needed first - a hysteroscopy, polyp removal or endometrial assessment.
• Whether sedation is required for the transfer.
• Insurance or employer cover, which some patients have for parts of fertility treatment.

Please call us on +91-8668954915 and we will give you a written estimate for your own plan, itemised, before you begin.

Preparing for your transfer

• Complete the pre-transfer tests we ask for - hormone profile, infection screening and an assessment of the uterine cavity.
• Take the medicines exactly as written, at the same times each day. Set alarms. Missed progesterone doses matter.
• Do not stop or change anything on your own, including supplements, on the advice of a relative or the internet.
• Keep other medical conditions controlled - thyroid, diabetes, blood pressure - because these genuinely affect implantation.
• Stop smoking and alcohol, both partners. This is one of the few things fully within your control that measurably helps.
• Come with a comfortably full bladder on transfer day - not painfully so. We will tell you when to drink.
• Skip perfume, deodorant and strong-smelling products on the day; the laboratory air is kept scrupulously clean.
• Bring your partner or someone you trust. The transfer is short but the day is emotionally long.
• Plan the two-week wait before it starts. Work, distraction, something to look forward to. The waiting is the part nobody prepares you for.

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If you have embryos in storage and are wondering when and how to use them - or if you are just at the beginning and trying to understand what IVF will ask of you - the fertility team at Shubham Hi-Tech Hospital and Test Tube Baby Centre, Amravati, will go through it with you slowly and without pressure. Call +91-8668954915 or get in touch here.

Disclaimer: This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor for guidance specific to your situation.