What Is Frozen Embryo Transfer (FET)?
FET is the transfer of a previously vitrified (flash-frozen) embryo into the uterus in a separate cycle from egg retrieval. It has become the most common type of embryo transfer at Korean clinics, accounting for 60–70% of all transfers.
Why freeze-all and do FET later?
- Allows ovaries to fully recover from stimulation
- Better endometrial receptivity in a non-stimulated uterus
- Time for PGT-A genetic testing results
- Schedule flexibility for international patients
- Higher cumulative live birth rates in many patient groups
FET Protocol Types
1. Medicated (Artificial) FET — Most Common
| Phase | Medication | Duration |
|---|---|---|
| Suppression (optional) | GnRH agonist nasal spray or injection | 2–4 weeks |
| Endometrial lining buildup | Oral estradiol (e.g., Progynova) | ~14 days |
| Progesterone start | Vaginal/intramuscular progesterone | Day –5 before transfer |
| Transfer | Embryo transferred | ~Day 20 of protocol |
Advantage: Fully controlled scheduling — ideal for international patients who need to plan travel precisely.
2. Natural Cycle FET
- No medications; relies on natural ovulation
- LH surge monitored via blood test or urine kit
- Transfer ~7 days after ovulation
- Best for women with regular cycles
- Slightly lower cancellation risk (no thick lining concern from meds)
3. Modified Natural Cycle
- Monitors natural development, then triggers ovulation with hCG injection
- Combines predictability with minimal medication
- Popular option at Korean clinics for regular-cycle patients
FET Timeline for International Patients
Medicated FET (Most Predictable for Travel)
| Day | What Happens | Location |
|---|---|---|
| Cycle day 1–2 | Start estrogen pills | Home country |
| Day 7–10 | Ultrasound check (lining thickness) | Home (send results) or Korea |
| Day 13–15 | Final lining check + progesterone start | Korea |
| Day 18–20 | Embryo transfer | Korea |
| Day 33–34 | Pregnancy blood test (beta-hCG) | Korea or home |
Minimum Korea stay for FET: 3–5 days
Many international patients start estrogen at home, coordinate a remote ultrasound with their local clinic, then arrive in Korea just for the final check + transfer.
What to Expect on Transfer Day
- No anesthesia required — transfer is typically painless (similar to a pap smear)
- Takes 10–15 minutes
- You'll be asked to have a full bladder (helps ultrasound visualization)
- Rest for 30–60 minutes in the clinic afterward
- Light activity is fine; no need for bed rest
- Continue progesterone medication exactly as prescribed
Endometrial Lining Targets
| Lining Thickness | Transfer Decision |
|---|---|
| ≥ 8mm (triple-layer pattern) | Proceed with transfer |
| 7–8mm | Proceed with caution; may adjust medication |
| < 7mm | Cycle may be postponed; medication adjusted |
If your lining doesn't thicken adequately, Korean clinics may add:
- Sildenafil (Viagra) — improves uterine blood flow
- Low-dose aspirin
- Estrogen patches (higher absorption)
- G-CSF (granulocyte colony-stimulating factor) for very thin linings
FET Success Rates in Korea
| Age at egg retrieval | FET live birth rate (per transfer) |
|---|---|
| Under 35 | 45–55% |
| 35–37 | 38–48% |
| 38–40 | 28–38% |
| Over 40 | 18–28% |
| Donor egg (any age) | 55–65% |
Euploid (PGT-A tested normal) embryos: add approximately 10–15% to above rates
Medications to Continue After Transfer
Your Korean clinic will prescribe a medication protocol. Typical regimen:
| Medication | Purpose | Duration |
|---|---|---|
| Progesterone (vaginal/IM) | Supports endometrial lining | Until 10–12 weeks if pregnant |
| Estradiol pills/patches | Maintains lining | Until 8–10 weeks if pregnant |
| Low-dose aspirin | Blood flow support | Often continued through 1st trimester |
| Progesterone support | Luteal phase support | Per clinic protocol |
Do not stop medications without doctor approval — premature discontinuation causes miscarriage.
FAQ
Q. Can I fly home immediately after FET?
Most clinics recommend staying 1–2 days after transfer for observation. Short-haul flights (2–4 hours) are generally fine after 24 hours of rest. Long-haul flights are better delayed 48–72 hours.
Q. How many embryos are transferred at Korean clinics?
Korean guidelines (and law) generally allow 1–2 embryos. Most clinics recommend single embryo transfer (SET) for women under 37 with good-quality embryos, as it reduces twin risk while maintaining high success rates.
Q. What happens to remaining frozen embryos?
They remain in cryostorage at the Korean clinic. Storage fees are typically ₩300,000–₩600,000/year. Embryos can be stored for up to 10 years (with annual consent), or shipped to a clinic in your home country.
📧 For hospital consultation and referral inquiries, contact: info@bronis.co.kr
Medical Disclaimer: This guide is for informational purposes only. Always follow your specific clinic's protocol instructions.