Frozen Embryo Transfer (FET)

Last updated: February 2026

What is FET?

Frozen embryo transfer uses embryos created and vitrified (rapidly frozen) during a previous IVF or ICSI cycle. The embryos are thawed and transferred to the uterus without repeating ovarian stimulation or egg collection.

Why it matters

In 2021, 43% of all embryo transfers in the UK were frozen (HFEA). That number has been climbing every year: it was 24% in 2013, 38% in 2019. In some Nordic countries, FET already exceeds fresh transfers. In the US, it’s over 80%.

Three things are driving the shift: vitrification survival rates above 95% (Rienzi et al., Human Reproduction Update, 2017), the rise of freeze-all strategies to reduce ovarian hyperstimulation syndrome (OHSS), and the need to freeze while waiting for PGT-A results.

Birth rates per frozen transfer are now comparable to fresh transfer rates across all age groups (HFEA, 2021). Some studies suggest frozen transfers may carry lower risks of preterm birth, low birth weight, and ectopic pregnancy compared to fresh (Maheshwari et al., Human Reproduction Update, 2018).

How it works

FET skips the hardest part of IVF. No injections for 2-4 weeks. No egg collection under sedation. The cycle takes 2-4 weeks from start to transfer, versus 4-6 for a full stimulated cycle.

Two approaches:

Natural cycle FET: Your own ovulation times the transfer. Monitoring via blood tests and ultrasound to detect the LH surge. Minimal medication. Works for patients with regular cycles.

Medicated FET: Estrogen builds the lining. Progesterone starts once it’s thick enough (typically 8mm+). Transfer date is precisely scheduled. Required for irregular cycles.

A Cochrane Review (Ghobara et al.) found no significant difference in live birth rates between the two. Protocol choice comes down to cycle regularity and scheduling convenience, not outcomes.

What to ask your clinic

• What is your embryo thaw survival rate?
• Do you recommend natural cycle or medicated FET for my case?
• How many embryos from my previous cycle are suitable for transfer?
• Will you recommend a single or double embryo transfer?

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Sources

1. HFEA. Freezing and Storing Embryos: https://www.hfea.gov.uk/treatments/fertility-preservation/freezing-and-storing-embryos/
2. HFEA. Fertility Treatment 2021: Preliminary Trends and Figures: https://www.hfea.gov.uk/about-us/publications/research-and-data/fertility-treatment-2021-preliminary-trends-and-figures/
3. Rienzi et al. Oocyte, embryo and blastocyst cryopreservation. Human Reproduction Update, 2017.
4. Maheshwari et al. Is frozen embryo transfer better for mothers and babies? Human Reproduction Update, 2018.
5. Ghobara et al. Cycle regimens for frozen-thawed embryo transfer. Cochrane Database of Systematic Reviews.
6. NICE Clinical Guideline CG156: Fertility Problems: Assessment and Treatment.

This page is for informational purposes only and does not constitute medical advice. Always consult a qualified fertility specialist before making treatment decisions.