How soon you reach transfer day depends on three things. One is how your clinic prepares your uterus. Another is what your scans and blood tests show. The third is whether you need tests or treatment before you start. Most of an FET cycle happens before the transfer, so the stages below show what to ask at each step. Your clinic's calendar always comes first. If something feels wrong, the warning signs are near the end.
What is a frozen embryo transfer?
In a frozen embryo transfer (FET), the lab thaws an embryo that was frozen earlier, and your doctor places it in your uterus. The embryo may have been frozen weeks or even years ago.
Frozen embryos can be made from:
- Your own eggs and your partner's sperm, in an earlier IVF cycle.
- Donor eggs, donor sperm or both.
- Donated embryos. Some programs let people give their unused frozen embryos to others.
A frozen blastocyst transfer uses an embryo frozen at the blastocyst stage. A blastocyst is an embryo that has grown for five to seven days and now has a few hundred cells.
The lining of the uterus is called the endometrium. It has to be the right thickness and in step with the embryo's age. Much of an FET cycle is about getting that timing right.
How long does an FET cycle take?
There is no single answer, because three things set the pace:
- The cycle type. A natural cycle follows your own ovulation, so the date isn't known at the start. A medicated cycle follows a medicine schedule. For a medicated cycle, Cleveland Clinic describes 14 to 21 days of hormone pills, then about six days of shots before the transfer. It lists two or three monitoring visits. Your clinic may use other forms, such as patches or vaginal progesterone.
- What monitoring shows. If your lining takes longer than expected to thicken, the transfer date can move, and you may need extra hormones and more scans. In a natural cycle, the plan waits for ovulation.
- Tests or treatment first. Some people need a test of the uterus first, such as a sonohysterogram. A problem like a polyp may need to be checked before a transfer.
Why have a frozen transfer?
Frozen transfers are very common. You may have embryos left over from a fresh cycle. Or a fresh transfer may be put off. Reasons include a risk of ovarian hyperstimulation syndrome (OHSS), a progesterone rise, genetic testing, or a lining problem. You can read more about freezing all embryos and how fresh and frozen transfers compare.
The three ways to prepare: natural, modified natural and medicated
Natural cycle FET. Your own hormones prepare the lining. The clinic tracks when you ovulate (release an egg) and plans the transfer a set number of days later. It works best with regular periods. See natural and modified-natural FET.
Modified natural FET. This is a natural cycle with a trigger shot, an hCG injection that helps time ovulation, so the transfer is easier to plan.
Medicated (programmed) FET. You take estrogen to build the lining. Then you add progesterone to get it ready for the embryo, and keep taking estrogen until your clinic says to stop. See medicated or programmed FET.
Natural cycles use fewer medicines, but they can need more monitoring and are cancelled more often. Medicated cycles are easier to schedule, though a slow lining can still move the date. Which costs less overall depends on your clinic's fees and how many visits and medicines you need.
A large 2026 trial in The BMJ studied 4,376 women aged 20 to 40 in China who ovulated regularly and were having one blastocyst transferred. The chance of a healthy live birth was similar with natural and medicated cycles. Among those whose pregnancy was seen on ultrasound, pre-eclampsia (a serious blood pressure problem in pregnancy) was less common after natural cycles. The results may not apply to people who don't ovulate regularly. Your doctor will weigh your cycle, your history and the clinic's schedule.
Your FET calendar, stage by stage
| Stage | What happens | Your checkpoint |
|---|---|---|
| Before you start | Some people need a test of the uterus first | Ask if you need any tests before your cycle |
| Start of the cycle | Your period marks the start. Medicated cycles start estrogen early in the cycle | Ask what to do when your period starts |
| Lining prep | Natural: your own follicle grows. Medicated: you take estrogen for a few weeks | Take each dose on time, or test for ovulation if told to |
| Monitoring | Ultrasound and sometimes blood tests check your follicle or lining | Go to every scan. Wait for the clinic's go-ahead |
| Timing set | Natural: ovulation or a trigger shot sets the date. Medicated: you start progesterone | Write down your progesterone start and transfer dates |
| Transfer day | The embryo is thawed that morning and placed in your uterus | Ask about a full bladder and getting home |
| Waiting | You keep taking any medicines you were prescribed | Do not stop any medicine on your own |
| Pregnancy test | A blood test, about 9 to 14 days after transfer | Get your result and next steps from the clinic |
Monitoring: scans and blood tests
A vaginal ultrasound measures the lining and checks its pattern. In a natural cycle, it also shows the follicle (the small sac where your egg grows). Blood tests may check hormone levels too.
If the lining is not ready, the clinic may change your medicine and scan again. In a natural cycle, a transfer may be cancelled if you don't ovulate as planned. That can be hard news after weeks of planning, so ask what it means for your embryos and when you could start again. Read more in cycle cancellation.
What happens on transfer day
The lab thaws your embryo that morning. Not every embryo survives thawing, and your clinic will tell you how yours did.
- No anesthesia is needed.
- A speculum is placed in the vagina, as for a Pap smear.
- A thin tube called a catheter goes through the cervix into the uterus, and the embryo is placed there.
- It usually takes less than 10 minutes.
Some clinics use an ultrasound on your belly to guide the catheter, so you may be asked to come with a full bladder. Whether you can drive home depends on any medicine you get that day and on your clinic's rules. Ask ahead, and arrange a ride if needed. Read more in embryo transfer day.
Does my age matter for a frozen transfer?
Two ages matter in different ways. An embryo stays the age it was when frozen. So the chance of success depends partly on your age when your eggs were collected. Your age now matters for the pregnancy itself, because the risk of pregnancy problems rises with age. For example, pre-eclampsia is more likely in people who get pregnant after 40. If years have passed since your eggs were collected, ask how that affects your pregnancy care.
After the transfer and the pregnancy test
Keep taking your medicines exactly as prescribed. In a medicated cycle, estrogen and progesterone go on until your pregnancy test, and for several more weeks if you are pregnant.
Mild bloating, cramps, sore breasts, spotting and constipation can happen. More on the wait is in after embryo transfer.
Your clinic checks for pregnancy with a blood test about nine to 14 days after the transfer. If it is positive, you may have more blood tests, then an ultrasound a few weeks later. If it is negative, your clinic will tell you when to stop your medicines. Ask when to expect a period, and what to do if it doesn't come.
Tips for your FET cycle
- Ask for your plan in writing, with the dates for scans, medicines and the transfer.
- Before you leave each visit, confirm your next dose and your next appointment.
- Set reminders for every dose, because the progesterone start sets the transfer date.
- If you get progesterone shots in the muscle, tell your clinic if the spot gets painful or looks infected.
- Keep the clinic's after-hours number in your phone.
When to get help
Call your clinic right away, day or night, if you have:
- A fever of 100.4°F (38°C) or higher.
- Bleeding from your vagina, or a brown, watery discharge. Light spotting can happen after a transfer. Still, let your clinic decide what it means.
- Belly or pelvic pain that is severe, gets worse, or isn't eased by the pain relief your clinic recommended.
- Pain and bloating in your belly, or bloating that is getting worse.
- Nausea and vomiting, nausea that won't go away, or you can't keep fluids down.
- Pain, redness or warmth in an arm or leg.
- Blood in your urine, or pain when you pee or poop.
Tell your clinic at your next contact about other milder symptoms that are new, don't go away or slowly get worse, such as sore breasts or mild cramps.