Single Embryo Transfer (SET)
Last updated: March 2026
What is single embryo transfer?
Single embryo transfer means “only one embryo is transferred to your womb instead of two or three” (HFEA). This approach “considerably reduces your chance of having a multiple birth” with “no significant impact on success rates” (HFEA).
Why it matters
Multiple pregnancies are the single biggest risk of fertility treatment. HFEA data: IVF twins are born before 37 weeks 60% of the time, versus 9% for singletons. They are 10 times more likely to need neonatal intensive care, 7 times more likely to die shortly after birth, and 6 times more likely to develop cerebral palsy (HFEA Multiple Births Report, 2019). SET eliminates most of this risk while maintaining live birth rates.
The numbers
| Year | UK multiple birth rate | SET rate |
|---|---|---|
| 1990s | ~28% | ~10% |
| 2007 | 26% | N/A |
| 2017 | 10% | N/A |
| 2023 | 3.4% | 88% |
(HFEA, 2023)
Birth rates continued to rise while the multiple birth rate collapsed. In 2023, 88% of UK IVF cycles used single embryo transfer (HFEA, 2023). Better blastocyst culture and vitrification for frozen embryo transfer made it possible to pick one good embryo and freeze the rest.
European regulation
Belgium was the first country to legislate. A 2003 law requires SET for women under 36 in exchange for government reimbursement of lab costs for up to 6 cycles. Result: twin pregnancies dropped from 19% to 3%, with no change in overall pregnancy rate (Bentley et al., 2005). Sweden mandated that only one embryo may be transferred unless the twin risk is assessed as low. Denmark, Norway, and Finland have strong professional guidelines favouring SET.
ESHRE’s 2024 guideline is unambiguous: “eSET should be the standard procedure whenever more than one embryo is available.” No clinical or embryological factor justifies double embryo transfer over SET. Cumulative live birth rates with SET are equivalent to DET, while multiple birth rates are dramatically lower (PMC10988112).
How SET fits into treatment
SET works best combined with blastocyst culture and PGT-A screening, allowing clinics to select the single strongest embryo. Surplus embryos are vitrified for future cycles. The cumulative live birth rate across fresh plus frozen transfers from one egg collection is comparable to transferring two embryos at once, without the twin risk.
What to ask your clinic
- Do you practise elective SET for my age group?
- What is your multiple birth rate? (If it’s above 10%, ask why.)
- How do you select which embryo to transfer?
- What happens to surplus embryos?
Comparing clinics? Get a personalised quote or estimate your costs.
Sources
- HFEA. Risks of Fertility Treatment: https://www.hfea.gov.uk/treatments/explore-all-treatments/risks-of-fertility-treatment/
- HFEA. Fertility Treatment 2023: Trends and Figures: https://www.hfea.gov.uk/about-us/publications/research-and-data/fertility-treatment-2023-trends-and-figures/
- HFEA. Multiple Births in Fertility Treatment 2019: https://www.hfea.gov.uk/about-us/publications/research-and-data/multiple-births-in-fertility-treatment-2019/
- ESHRE Guideline on Elective Single Embryo Transfer, 2024: https://pmc.ncbi.nlm.nih.gov/articles/PMC10988112/
This page is for informational purposes only and does not constitute medical advice. Always consult a qualified fertility specialist before making treatment decisions.