Why should I recommend single embryo transfer (SET)?

To understand why single embryo transfer(SET) should be recommended where appropriate, it is necessary to be aware of:

• the facts about the rising number of multiple births.
• the risks of multiple pregnancy and birth to both mother and child.
• the increasing success rates of single embryo transfer.
• the pressure that the rising number of premature twins is causing to children´s services.

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On this page:

• Fertility treatments and rising twin birth rates  
• Multiple embryo transfer and the high incidence of twin births 
• Risks associated with multiple pregnancy and birth 
• Effect of multiple pregnancy and birth on children's services 
• Effect of elective single embryo transfer (eSET) on live birth rates

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Fertility treatments and rising twin birth rates

The evidence that the rise in assisted reproductive technologies (ART) is accompanied by an increase in the number of twins is undeniable.

• The number of in vitro fertilisation (IVF) and intra-cytoplasmic sperm injection (ICSI) babies has risen dramatically in recent decades, accompanied by a rise in the number of twins born after IVF.
• The 2003/04 Human Fertilisation and Embryology Authority (HFEA) register gives a 23.6% rate of multiple births after IVF. This is more than ten times higher than would be expected after natural conception. Around 25% of all twins born in the UK are to mothers who had IVF treatment.
• The latest HFEA register demonstrates the link between IVF and multiple pregnancy and birth; however, other forms of fertility treatment, such as hormone treatment and IUI also have an effect. International studies have estimated that about 25% of twins born each year are the outcome of treatment with ovulation drugs or intrauterine insemination (IUI).

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Multiple embryo transfer and the high incidence of twin births

Transferring more than one embryo during IVF/ICSI is a major cause of the high twin rate. 

• The high twin rate after IVF/ICSI is caused by the number of embryos transferred during IVF. Although the incidence of identical twins is increased after IVF (the risk is 2–5 times greater after receiving fertility treatment than after natural conception), most IVF twins are non-identical: they come from 2 different embryos that were simultaneously transferred to and implanted in the womb.

Risks associated with multiple pregnancy and birth

Multiple pregnancies and births are the single biggest risk to mothers and children during IVF treatment. For detailed information on the risks to both mothers and children that are associated with multiple pregnancy and birth.   For more information see What are the risks?.

It should be stressed that the high incidence of IVF twins would be avoided if SET was used for suitable patients. IVF children would then have almost the same chance as naturally conceived children of being born as full-term and normal birth weight singletons.
 

Effect of multiple pregnancy and birth on children´s services

The rising numbers of twins is resulting in increasing pressure on neonatal and paediatric services:

• Because they are born early, 40–60% of twins are admitted to neonatal care when they are born  and more than 10% spend more than 4 weeks there. This is almost 10 times more than for singleton babies.
• A recent survey by the baby charity Bliss found that many neonatal units do not have sufficient staff and resources to care for the numbers of babies who need special, high dependency or intensive care. This may result in unsafe situations and over 70% of units have had to close their doors to admissions at times.
• It is not unknown for this pressure on resources to result in a situation where the mother and children receive care in three separate hospitals.
• One UK study points out that if just the money spent on IVF triplets in the first year of their lives was saved, that money could buy almost 2000 extra cycles of IVF for the NHS. Even more could be redirected into providing IVF cycles if SET was introduced for an appropriate sub-group of patients.

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Effect of elective single embryo transfer (eSET) on live birth rates

In countries where eSET is more widely used, experience shows that when given to suitable patients and followed up by treatment with frozen embryos, eSET has little effect on the live birth rate, when compared with multiple embryo transfer.

However, in the UK, the availability of funding for follow-up treatment with frozen embryos varies. For more information see Defining a cycle.

In 2003 Sweden had the greatest use of SET and the lowest multiple birth rate, but still ranked 4th on live birth rates. Sweden´s multiple birth rate is now below 5%. 

• Evidence from Sweden shows that good live birth rates aren´t necessarily dependent upon a higher multiple birth rate. 
• A Cochrane review of the available randomised controlled trials concluded that eSET significantly reduces the risk of multiple pregnancy, but also decreases the chance of live birth in a fresh IVF cycle. Subsequent replacement of a single frozen embryo achieves a live birth rate comparable with double embryo transfer.
• Observational studies have recently been reviewed and summarised by two authors: Bergh (2005) and Gerris (2005). Bergh concluded that the pregnancy rates were the same in eSET and double embryo transfer (DET) groups, but this was because ´good prognosis women receive eSET while poor prognosis women receive DET.´ Gerris concluded that cryopreservation is an important tool for maintaining success rates after eSET and that transferring the ´2 best´ embryos always yields more pregnancies than transferring only ´the best embryo´. For more information see Research. 
• To maintain pregnancy rates with eSET, it is important to be able to choose the embryo with the highest chance of implantation for the initial transfer.
  Embryo selection is also a crucial part of a
  successful embryo freezing programme. For more information see Embryo grading.
• In a recent UK study of over 2,000 fresh IVF cycles in which 5-day old blastocysts were transferred, only one in 11 (118/1253) cycles had an elective single blastocyst transfer. However, by focusing eSET on cycles at high risk of multiple pregnancy and birth, the multiple pregnancy rate was almost halved while the overall pregnancy rate was slightly increased - refer to the below graph.

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