Preparing for a frozen embryo transfer (FET) typically takes six to eight weeks from start to finish, and most of that time is spent getting your uterine lining ready to receive the embryo. The process involves hormonal medications, monitoring appointments, and some lifestyle adjustments, but understanding each phase makes it far more manageable.
How the FET Cycle Begins
A medicated FET cycle often starts with three to four weeks of daily birth control pills. This might seem counterintuitive when you’re trying to get pregnant, but the purpose is to suppress your natural ovarian cycle so your clinic can control the timing precisely. Without suppression, your body could ovulate on its own and throw off the carefully planned schedule.
After finishing birth control, you’ll go in for a baseline assessment: bloodwork and an ultrasound to confirm your ovaries are quiet and your lining is thin, essentially a blank slate. If everything looks good, the next phase begins.
Medicated vs. Natural Cycle Protocols
Your doctor will recommend one of two main approaches, depending on whether you ovulate regularly and your medical history.
In a medicated cycle, you take estrogen (pills, patches, or injections) to build your uterine lining from scratch, followed by progesterone to make that lining receptive. Your ovaries stay suppressed the entire time, giving your clinic full control over timing. This is the most common protocol because it’s predictable and easy to schedule.
In a natural cycle, your body ovulates on its own, and the transfer is timed around that natural surge. You may still take some progesterone for support, but your own hormones do most of the work. A study published in Fertility and Sterility found that natural cycle transfers had significantly higher ongoing pregnancy rates compared to medicated transfers (60.7% vs. 42.9%) when using genetically tested embryos. Natural cycles require more frequent monitoring to catch ovulation, which makes scheduling less flexible, but some doctors prefer them for patients who ovulate reliably.
If you have conditions like endometriosis or adenomyosis, your doctor may add a period of ovarian suppression before starting the cycle. The hormonal suppression can help quiet inflammatory changes in the uterine lining that might otherwise interfere with implantation.
Building and Monitoring Your Lining
The uterine lining is the single most important factor your clinic tracks during preparation. In a medicated cycle, estrogen thickens it over roughly two weeks. You’ll return for at least one ultrasound and blood draw during this phase so your doctor can measure the lining and check hormone levels.
The target is a lining of at least 7 millimeters. A large analysis of over 96,000 embryo transfers found that live birth rates in FET cycles increased as the lining thickened up to about 7 to 10 mm, then plateaued. Anything under 6 mm was associated with a dramatic drop in the chance of a live birth. If your lining isn’t thickening on schedule, your clinic may adjust your estrogen dose or extend the priming period.
Some women have persistently thin linings. Small studies suggest that vitamin E at 100 to 200 IU daily may help support lining growth, though the evidence is limited. Don’t add supplements on your own. If your lining is a concern, your doctor can recommend specific interventions.
Starting Progesterone
Once your lining is thick enough and your hormone levels look right, you’ll add progesterone. This is the medication that transforms the lining from “growing” mode to “receptive” mode, opening the window when the embryo can implant.
Timing matters here. For a blastocyst-stage embryo (the most common type transferred in FET), you’ll typically take progesterone for five to six days before the transfer. For cleavage-stage embryos, it’s three to four days. Your clinic will give you a precise schedule because even a day off can affect receptivity.
Progesterone comes in several forms. Vaginal suppositories, gels, or capsules are common, typically at 100 to 200 mg taken one to three times daily. Intramuscular injections (the daily shots into the upper buttock) are another option. Many clinics use a combination of both. Oral progesterone is less common for FET because the liver breaks it down before enough reaches the uterus.
You’ll continue both estrogen and progesterone through the transfer and for about two weeks afterward, until your pregnancy blood test. If the test is positive, you’ll stay on these medications into the first trimester.
Does Genetic Testing Change Your Odds?
If your embryos were genetically tested (PGT-A), your success rates look different than if they weren’t. Tested embryos have a consistent implantation rate of roughly 48 to 58% regardless of age. Untested embryos start around 47% at age 31 but decline steeply, dropping to under 9% by age 43.
The practical takeaway: if you’re transferring a genetically tested embryo, your age at the time of transfer matters much less. The embryo’s genetics were locked in when it was created. If you’re transferring an untested embryo, your original age at egg retrieval plays a bigger role in expected outcomes.
What to Do in the Weeks Before Transfer
Beyond medications, the preparation period is a good time to focus on a few controllable factors. Avoid intense exercise or anything that significantly raises your core body temperature, like hot tubs or saunas. Moderate activity like walking is fine and encouraged. Alcohol is best avoided during the medication phase, and smoking (including cannabis) should be stopped well before a cycle begins.
Sleep matters more than most people realize. Consistent, adequate sleep supports the hormonal environment your medications are trying to create. Stress reduction isn’t just a nice idea; chronic stress can alter blood flow to the uterus. Whatever helps you decompress, whether that’s walking, meditation, or something else entirely, is worth prioritizing.
Transfer Day: What to Expect
The transfer itself is quick, usually taking about 10 to 15 minutes. You don’t need to fast. Eat and shower as usual that morning. There are a few specific instructions worth knowing:
- Full bladder: About an hour before your appointment, drink four to five glasses of water. A full bladder helps the doctor see your uterus on ultrasound and positions it for easier catheter placement.
- No scented products: Skip cologne, scented lotion, hair gel, and powder. Embryos are sensitive to volatile chemicals in the lab environment.
- Bring warm socks: Procedure rooms are cold, and you’ll be in a gown from the waist down.
- Arrive early: Plan to get there about 30 minutes before your scheduled time to check in and change.
You’ll be awake the entire time. The doctor threads a thin catheter through your cervix and places the embryo using ultrasound guidance. Most women describe it as similar to a Pap smear, with mild pressure but rarely any significant pain.
After the Transfer
You don’t need strict bed rest. Older guidance recommended lying flat for hours or even days, but current evidence shows that prolonged bed rest doesn’t improve implantation rates. A short rest at the clinic (usually 15 to 30 minutes) is standard, and then you can go home.
For the first 24 to 48 hours, take it easy. Light activity around the house is fine, but skip anything strenuous. For the full two weeks before your pregnancy test, avoid vigorous exercise like running or high-impact aerobics. Don’t lift anything over 10 to 15 pounds, and avoid movements that create significant abdominal pressure. Gentle walking and light yoga are good alternatives.
Most clinics recommend avoiding sexual intercourse for at least 48 hours after the transfer to prevent any disruption to early implantation. Your clinic may have a longer recommendation depending on your specific situation.
Continue your estrogen and progesterone exactly as prescribed. Missing doses during this window can cause your lining to shed prematurely. Set alarms if you need to, especially for medications that require specific timing. Your pregnancy blood test will be scheduled roughly 10 to 14 days after the transfer.