Benefits of single embryo transfer (SET)
How does single embryo transfer work?
Your clinic will recommend single embryo transfer (SET) if they feel it is the best option for you, and if they are confident that your embryos are healthy and likely to implant. This is because you are more likely to become pregnant with twins or more babies if more than one embryo is transferred.
In Sweden, where SET is more widely used, recent research shows that, in appropriate patients, pregnancy rates are maintained when frozen follow-up treatment is included. For some women, the chances of becoming pregnant seem to be even higher with blastocyst transfer than with cleavage stage embryo transfer.
The procedure
The procedure for SET is the same as that for conventional IVF or ICSI (in vitro fertilisation or intra-cytoplasmic sperm injection) – the only difference is that only one embryo is transferred:
- As with stimulated IVF, the woman is given hormones to increase her egg production.
- When the eggs are mature, they are collected from the ovaries and then mixed with sperm (or for ICSI, a single sperm is injected into each egg).
- The fertilisation is monitored for two to three days, enabling an embryologist to carefully select the embryo that is most likely to implant itself in the womb. Some clinics may also offer blastocyst transfer, where the fertilised eggs are left to mature for 5 to 6 days.
- One embryo, selected by the embryologist as having the best chance of implantation, is transferred to the woman’s womb.
- Any remaining embryos that the embryologist selects as having a good chance of implantation are frozen and stored.
- If the woman does not become pregnant, the frozen embryos are thawed and transferred until the woman becomes pregnant or all the embryos have been used.
The expert says...
"Multiple births as a result of IVF increase the risks of death and disability, not only from the more complex pregnancy and delivery, but also from prematurity. The best way to ensure a healthy baby and avoid the trauma of neonatal intensive care is by single embryo transfer."
Dr Alun Elias-Jones, Consultant Community Paediatrician, Leicester
Why consider single embryo transfer?
If you are a suitable patient and single embryo transfer (SET) or single blastocyst transfer (SBT) is correctly administered, it largely removes the risks of multiple pregnancy without significantly reducing your chance of a successful outcome.
The issues to consider are:
- The risks are that multiple pregnancy can have serious, even fatal consequences for both mother and children. Multiple birth is still the single biggest risk to the health and welfare of children born after IVF (See What are the risks?).
- Research from other countries that use SET more widely than the UK, such as Sweden, shows that success rates did not fall when SET was used for a higher percentage of treatments, provided frozen follow-up treatment was included.
- However, if fresh embryo transfer is not successful, you may have frozen embryos transferred in later follow-up treatment. Although this may take longer and add to the cost, if you are at high risk of multiple pregnancy, you should consider the benefits SET can offer.
Is single embryo transfer right for me?
Single embryo transfer (SET) is not suitable for everyone and your clinic will only recommend it if they consider you to have a good chance of conceiving and therefore to be at high risk of multiple birth. The type of criteria your clinic is likely to use to decide whether you are suitable for SET are:
- You are under 37.
- You are able to produce at least one good quality embryo.
- You are undergoing your first or second IVF treatment (that is, you don’t have an extended history of failed IVF attempts).
Other factors may affect your clinic’s recommendation, such as whether you suffer from endometriosis or tubal disease, so you should always discuss any concerns you have with your clinician.
