Frozen embryo transfer
Why freeze-all is increasingly used
ESHRE (2026) makes freeze-all a strong recommendation to minimise the risk of late-onset OHSS, and recommends a GnRH agonist trigger combined with freeze-all in women at risk of OHSS.
Where a GnRH agonist protocol with hCG trigger is used in high responders, freeze-all is recommended to reduce late-onset OHSS.
There is also a new recommendation relevant here: serum progesterone should probably be measured on the day of trigger in cycles planning a fresh transfer. Where it is high, you should be counselled about potentially lower pregnancy rates — and the decision whether to defer transfer weighed alongside oocyte number, embryo number and quality.
So a decision to freeze rather than transfer fresh is often a considered one rather than a setback.
Endometrial preparation
Three broad approaches — natural cycle, modified natural cycle, and programmed (hormone replacement) cycle.
The ESHRE stimulation guideline does not cover endometrial preparation, and I am not aware of a verified recommendation favouring one. The practical trade-offs:
Programmed cycles offer scheduling flexibility, which matters for travel and clinic capacity. They require luteal support, and inadequate luteal support is a recognised and correctable cause of failure — worth asking about specifically.
Natural and modified natural cycles rely on your own ovulation, so timing is less flexible, but luteal function is your own.
Survival and quality
Blastocyst cryosurvival benchmarks from the Vienna Consensus: competency at least 90%, benchmark at least 99%.
Ask your clinic for their own cryosurvival rate. It is a meaningful quality indicator and they should have it.
Practical points
The transfer itself is brief and requires no anaesthetic. Afterwards, bed rest does not improve success rates — normal activity is fine.
Where freeze-all followed OHSS risk, symptoms can persist for a while after retrieval, and transfer is generally deferred until you have recovered.
If you have several frozen embryos
Ask how they will be ranked for transfer. Grading is one input — from the Vienna Consensus, trophectoderm appearance was the statistically significant independent predictor of live birth. But grading systems are described as not robust and better suited to internal quality assessment than comparison.
One question worth settling early
What happens to remaining embryos — storage duration, cost, and what occurs if you move, if the clinic closes, or if you stop paying. Get the answer in writing before you start.
Frequently Asked Questions
Is frozen embryo transfer better than fresh?▾
For most patients, FET achieves equal or slightly higher live birth rates than fresh transfer. Fresh transfer in a stimulated cycle may expose the embryo to a hormonally disrupted uterine environment. The main exception is poor responders with few embryos — for them, fresh transfer avoids the small risk of embryo loss during freezing, though vitrification survival is >95%.
How long does a FET cycle take?▾
The FET procedure itself takes 10–15 minutes and requires no anaesthetic. The preparation takes 4–6 weeks — about 2–3 weeks for a natural cycle FET, or 12–16 days of hormone preparation for a medicated FET. Total from starting hormones to pregnancy test: approximately 4–6 weeks.
What should I do after a frozen embryo transfer?▾
Resume light normal activities. There is no evidence that bed rest improves outcomes. Avoid strenuous exercise, alcohol, and NSAIDs. Continue prescribed progesterone and estrogen (if on medicated protocol) exactly as directed. The beta-hCG pregnancy blood test is done 10–14 days after transfer.