What is a frozen embryo transfer (FET), and what does the cycle involve?
A frozen embryo transfer (FET) places an embryo, frozen after IVF, into the womb in a later cycle. The lining is first built up, usually with estrogen tablets and scans over about two weeks. Progesterone is then started, the thawed embryo is transferred on a planned day, and a pregnancy blood test follows about two weeks later.
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Many IVF cycles now end with embryos safely frozen rather than transferred straight away. That raises new questions for a couple: why wait, what happens next, and which medicines are involved? In this video, in Hindi, Dr Mayur Pai explains the frozen embryo transfer cycle, shows the tablets and injections used, and shows on ultrasound what a well-prepared womb lining looks like.
What is a frozen embryo transfer?
During IVF, embryos are grown in the laboratory from the collected eggs and the husband's sperm. Good embryos that are not transferred straight away are frozen by a rapid method called vitrification and stored safely. In a frozen embryo transfer, the embryo chosen for transfer is thawed and placed in the womb in a later cycle, once the womb has been carefully prepared. To see how the embryos are made in the first place, read the IVF process explained step by step.
Why are embryos frozen instead of transferred fresh?
There are several good reasons, and the doctor chooses what is safest and most sensible for you:
- Hormones out of step. If a hormone such as progesterone has risen too early by the time of egg collection, the lining may no longer match the embryo. A calmer cycle is better.
- PCOS and over-stimulation. Polycystic ovaries can over-respond to stimulation, and transferring an embryo in the same cycle can make ovarian hyperstimulation worse, with fluid collecting in the tummy or chest. Freezing all the embryos lets the ovaries settle first. How eggs develop in PCOS.
- Collecting over more than one cycle. When the egg reserve is low, or age is higher, eggs may be collected over two or more cycles and the embryos stored, then transferred later.
- Family logistics. Many husbands in Goa work abroad and come home only for short visits. The eggs can be collected and the embryos made while he is here, and the transfer done later.
- Spare embryos. After a fresh transfer, any extra good embryos can be frozen for a later attempt or a future brother or sister.
When does the FET cycle start?
Usually after one or two periods following egg collection, once the ovaries have settled. The cycle begins with a period: you let us know when it starts, and the plan begins from an early day of that period. Nothing needs to be rushed, because the embryos stay safely frozen until the womb is ready.
Preparing the lining: the most important step
The embryo needs a womb lining that is thick, healthy and ready at the right moment. On ultrasound, a well-prepared lining shows a clear "triple line": a bright centre line with a line above and below it. Building that pattern is the main work of an FET cycle.
Most often the lining is prepared with estrogen tablets, taken daily from the start of the cycle. You come for a vaginal scan every few days, and the doctor checks the thickness of the lining, its triple-line pattern and the blood flow to the womb. The lining is usually ready in about two weeks, though some women need longer, and the plan is adjusted if it grows slowly. In some women with regular cycles, the doctor may instead time the transfer to their own natural ovulation, tracked with scans.
The medicines, in plain terms
An FET cycle mainly uses three groups of medicines. Your doctor decides which you need, in what form and how much; this is only an overview.
- Estrogen, usually tablets, builds up the lining.
- Progesterone makes the lining receptive to the embryo. It is started once the lining is ready and given as injections, vaginal capsules or tablets. Take it at the same time every day.
- Blood thinners, as tablets or injections, are added only for some women, when the doctor feels the blood flow to the womb needs support. They are not routine.
How the transfer day is chosen
The transfer is timed from the day progesterone begins, to match the age of the embryo. An embryo frozen on day three and a blastocyst frozen on day five are transferred on different days of progesterone, so that the embryo and the lining are in step, just as they would be in nature. On the morning of the transfer, the embryologist thaws the embryo and checks it before it is placed.
What happens on transfer day?
The transfer is very similar to an IUI. You lie as for an internal examination, and a very soft, thin tube carrying the embryo is passed gently through the neck of the womb, guided by scan, to place the embryo in the middle of the womb. Most women need no anaesthesia; for the few who find the examination very uncomfortable, a short anaesthetic can be used. It takes a few minutes, and after a short rest you go home.
The two-week wait
After the transfer, keep taking the estrogen and progesterone exactly as prescribed. Do not stop or change any medicine on your own, even if you notice spotting; call us instead. About two weeks after the transfer, a beta hCG blood test shows whether the embryo has implanted. If it is positive, the medicines are usually continued for a while, and the doctor tells you when and how to stop them. Normal light activity is fine, and strict bed rest is not needed. See how this compares with a fresh cycle in the IVF timeline, week by week.
What affects the result?
The chance of a pregnancy depends mainly on the quality of the embryo, the woman's age when the eggs were collected, and the health of the womb. Problems inside the womb, such as fibroids or polyps, can lower the chance, so the doctor may advise treating them before a transfer. We do not quote general figures; after reviewing your embryos and scans, the doctor explains what is realistic for you.
About this guide
This guide is by Dr Mayur Pai, MBBS, MS (Obstetrics & Gynaecology), a fertility and laparoscopy specialist. Pai Hospital in Goa has its own operating theatre and its own IVF laboratory, so the scans, the embryo freezing and thawing, and the transfer all happen in one place, under one team.
Questions, or ready to book?
Have frozen embryos and wondering what the next step is? Send your question and any reports on WhatsApp to +91 95185 02773. To book a consultation, call Sheetal at our fertility reception on +91 95459 20817; every visit is by appointment. Consultations are held in Panjim, Margao, Mapusa and Vasco. Our frozen embryo transfer packages are transparent and fixed; ask us and we will explain exactly what is included.
This article is for education only and is not personal medical advice; please consult your doctor about your own situation.
Your questions
How soon after egg collection can a frozen embryo transfer be done?
Usually after one or two periods, once the ovaries have settled. The cycle starts with a period, and the lining is then prepared over about two weeks before the transfer.
Do I need injections in a frozen embryo transfer cycle?
Not always. The lining is usually prepared with estrogen tablets. Progesterone may be given as injections, vaginal capsules or tablets, and blood-thinning injections are added only for some women, when the doctor advises them.
Does a frozen embryo transfer need anaesthesia?
Most women need none. The transfer feels much like an internal examination or an IUI and takes a few minutes. If the examination is very uncomfortable for you, it can be done under a short anaesthetic.
Why did my doctor advise freezing all our embryos?
Usually for safety or timing: for example, a high risk of over-stimulation with PCOS, hormone levels that rose too early during stimulation, or a plan to collect eggs over more than one cycle. Freezing lets the transfer happen later, in a calmer cycle, when the womb is ready.
Do I need bed rest after a frozen embryo transfer?
No. Normal light activity is fine after a short rest on the day. What matters most is taking the estrogen and progesterone exactly as prescribed, and calling us, rather than stopping any medicine, if you notice spotting.
Or call +91 95185 02773
This page is for general education and is not personal medical advice. Treatment depends on your own examination and reports, so please speak to a doctor about your situation. We do not carry out or offer sex determination of any kind.