Medicated frozen embryo transfer: estrogen, progesterone and timing

In a medicated FET, the day you start progesterone sets your transfer date, so that is the instruction to check most carefully. Before it, you take estrogen for a few weeks to build the lining of your uterus. After it, you keep taking both until the stop date your clinic gives you, because in this kind of cycle the medicines do the job your ovaries would normally do. This plan is easier to schedule than a natural cycle, but a lining check or blood test can still move the date. The warning signs are near the end.

What is a medicated FET?

A medicated FET is also called a programmed or hormone replacement cycle. Instead of relying on your own ovulation, you take hormones that do the job your ovaries would do.

• Estrogen thickens the lining of your uterus, called the endometrium.
• Progesterone then changes the lining so an embryo can attach.

The embryo is placed when the lining and the embryo are in step. For an overview of all FET types, see frozen embryo transfer.

Who is a medicated FET for?

This plan is often used for people with irregular cycles, people past menopause, and donor egg cycles. People with regular cycles may have it too, since the timing is easier to plan.

Medicated cycles are cancelled less often than natural cycles. Still, the date is not fixed. If your lining is slow or a hormone result is off, your clinic may change the plan. Natural cycles use fewer medicines. If you want to compare, read about natural and modified-natural FET.

How does it compare with a natural cycle?

In January 2026, The BMJ published a randomized trial from 24 fertility centers in China. It included 4,376 women aged 20 to 40 who had regular cycles, ovulated on their own, and were having one frozen blastocyst transferred. Half were assigned a natural-ovulation cycle and half a medicated cycle.

• Healthy live birth (one baby born at 37 weeks or later, at a normal weight, without major birth defects): 41.6% in the natural group and 40.6% in the medicated group. The trial counted these as similar.
• Pre-eclampsia, a serious blood pressure problem in pregnancy: among those whose pregnancy was seen on ultrasound, 2.9% after natural cycles and 4.6% after medicated cycles.
• Cancelled cycles (on the first try at preparing the lining): 16.2% of natural cycles and 11.5% of medicated cycles.

The authors say the results may not apply to people with ovulation problems, a thin lining, repeated failed transfers or scarring inside the uterus. Ask your doctor how these results fit your own situation.

Step 1: Estrogen builds the lining

Estrogen starts early in your menstrual cycle. It can come as pills, patches or shots, and your clinic chooses the form. In an international survey, pills by mouth were used most often. Patches and vaginal forms give similar results.

Cleveland Clinic describes about two to three weeks of hormone pills. Your clinic may make this phase shorter or longer, depending on your lining.

Some clinics also use a medicine first to pause your own hormone signals. This step is optional, and pregnancy rates are similar with or without it.

Estrogen can make your breasts feel tender. It may also raise the risk of blood clots, so tell your clinic if you have ever had a clot.

Step 2: Lining check

Next you have a vaginal ultrasound. It measures how thick your lining is and checks its pattern. You may also have blood work to check your hormone levels.

If the lining is not ready, your clinic may adjust your treatment or check why it isn't responding as expected. That can mean extra hormones, more scans and a later transfer, which may add cost. Ask how a change affects your calendar and your medicine supply.

Step 3: Progesterone and the transfer date

Once the lining is ready, the clinic tells you when to start progesterone. The transfer is set for a certain number of days after that start, based on your embryo's age. Write the date down and check it with the clinic.

Progesterone comes in several forms. It can be a shot into a muscle (often called PIO, short for progesterone in oil) or a vaginal gel, insert or pill. Forms taken by mouth or under the skin are also used, but there is less research on them. Your doctor decides which one is best for you, and the forms are not simply swapped for one another. If you can't use the one you were given, call your clinic, and change only on its instructions.

Before you start, make sure you know:

• The exact name and form of your progesterone.
• How and when to use it.
• Whether there is an alternative for you if you can't use it.

Shots in the muscle can cause pain where you inject, and sometimes infection. Tell your clinic about soreness or a spot that worries you.

Take every dose on time. After a natural ovulation, the corpus luteum (the part of the ovary left after the egg is released) makes progesterone. In a medicated cycle there is no corpus luteum, so your doses do that job.

Step 4: Transfer day

The embryo is thawed the morning of the transfer and placed in your uterus with a thin tube. It needs no anesthesia and takes less than 10 minutes. You may be asked to come with a full bladder so the doctor can see on ultrasound. See embryo transfer day for the details.

Step 5: Pregnancy test and beyond

Your clinic checks for pregnancy with a blood test about nine to 14 days after the transfer.

If the test is positive, you keep taking estrogen and progesterone for several more weeks. Because there is no corpus luteum, clinics commonly continue progesterone until about the 10th to 12th week of pregnancy. Your clinic gives you a stop date for each medicine. Follow that date, not the day a package runs out or the day you feel ready, because stopping early takes away hormones your lining still relies on.

If the test is negative, your clinic will tell you when to stop. Ask when to expect a period and what to do if it doesn't come.

Medicated FET timeline at a glance

Stage	What happens	Checkpoint
Start	Estrogen begins early in your cycle	Confirm the start day and form
Building	Estrogen every day	Same times each day
Lining check	Ultrasound and maybe blood work	Wait for the clinic's call
Progesterone starts	The form your doctor chose	Write down the start date
Transfer	A set number of days into progesterone	Confirm the time and bladder instructions
Waiting	Both medicines continue	Don't stop anything
Pregnancy test	Blood test	Ask for the stop date of each medicine

Your medicated FET checklist

• Get your calendar in writing: estrogen start, scan dates, progesterone start and transfer day.
• Pick up your medicines before you start, with enough to last past your test.
• If you have shots, ask the clinic to show you or your partner how to give them.
• Ask now what to do if a patch comes off or you miss a dose.
• Set an alarm for every dose, and write down any missed or late dose.
• Before you leave each visit, confirm your next dose and next appointment.

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 soreness where you inject.