Embryo transfer and multiple births

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How many embryos are transferred in each treatment cycle?

The number of embryos transferred in each IVF or ICSI treatment cycle has changed dramatically since 1992 when 60 in every 100 transfers carried out involved three embryos (60%). 

The single greatest health risk for women conceiving following fertility treatment is a multiple pregnancy. The risk of multiple births can be reduced by transferring fewer embryos.  

Changes in embryo transfer policy

From 1991 onwards, clinics in the UK were expected to transfer no more than three embryos in each cycle. Over the 1990s it became more common for clinics to transfer only two embryos and the percentage of treatment cycles involving a three embryo transfer declined dramatically.

In 2001 the HFEA introduced a two-embryo transfer policy for women under the age of 40 years. In exceptional circumstances only, three embryos were allowed to be transferred.

In 2004 this policy was revised so that now a maximum of two embryos can be transferred to women under the age of 40, with no exceptions, and a maximum of three can be transferred in women aged 40 and over.

Since 2004 only 4 in every 100 treatment cycles (4%) performed involved three embryos being transferred.

New HFEA policy

The HFEA is now working in partnership with professional bodies, patient groups and clinics on a ‘National Strategy’ to reduce multiple pregnancies from all fertility treatments. As part of this, the HFEA introduced a policy in 2008 which aims to bring down the UK IVF mulitple birth rate to 10% over a staged period.

 

 Number of embryos transferred (ET) per IVF and ICSI treatment cycle,
treatment cycles started 1992 to 2007

Graph showing number of embryos transferred (ET) per IVF and ICSI treatment cycle 1992-2007

Note: The figures given for ICSI treatment include those for SUZI cycles. What is SUZI? 

Two embryos were transferred in 30 in every 100 (30%) treatment cycles performed in 1992, whereas by 2007 this has increased to 81 in every 100 (81%).

In the past single embryo transfer was generally carried out when there was only one embryo available to transfer and accounted for only 13 in every 100 treatment cycles performed (13%).

Following a decline in single embryo transfer to 8 in every 100 (8%) treatment cycles in 2001, the percentage increased steadily again to nearly 15 in every 100 (15%) by 2007.

Some of these single embryo transfers now include ‘elective’ single embryo transfer.  This is where only one embryo is transferred during a cycle, even though the patient may have several embryos available.

A clinic will recommend elective single embryo transfer if they feel it is the best option for a patient, and if they are confident that their embryos are healthy and likely to implant. A single embryo is transferred when the risk of conceiving a multiple pregnancy following a two-embryo transfer is high. 

 

Number of embryos transferred (ET) in IVF and ICSI treatment cycles carried out in 1992 and 2007:

    Graph showing number of embryos transferred (ET) in IVF and ICSI treatment cycles 1992 & 2007

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How many women have had singleton and multiple births?

The number of women giving birth to a singleton (a single baby) has more than quadrupled between 1992 and 2006:

  • Treatment started in 1992 – 1,715 singleton births
  • Treatment started in 2006 – 7,938 singleton births

The total number of women having a multiple birth following IVF and ICSI treatment has increased over time, in line with the general increase in women undergoing fertility treatment and babies born.

The number of women giving birth to multiples (twins, triplets and higher order multiples) has more than trebled between 1992 and 2006:

  • Treatment started in 1992 – 664 women had multiple births
  • Treatment started in 2006 – 2,312 women had multiple births

The HFEA is now working in partnership with professional bodies, patient groups and clinics on a ‘National Strategy’ to reduce multiple pregnancies from all fertility treatments. As part of this, the HFEA introduced a policy in 2008 which aims to bring down the UK IVF mulitple birth rate to 10% over a staged period.

 

Total number of women giving birth to singletons and multiples following IVF and ICSI treatment cycles started in 1992 to 2006:

Graph showing total number of women giving birth to singletons and multiples following IVF and ICSI treatment 1992-2006

Note: The figures given for ICSI treatment include those for SUZI cycles. What is SUZI?
Figures for live births refer to babies who were still alive at one month of age. They include singleton births and multiple births.

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What proportion of births after IVF or ICSI are singletons and multiples?

The chance of conceiving and giving birth to a multiples (twins, triplets and more) increases with the number of embryos transferred during IVF or ICSI. The single greatest health risk for women conceiving following fertility treatment is a multiple pregnancy.

The total number of women having a multiple birth after IVF or ICSI treatment has increased over time, because of the increasing number of treatment cycles carried out. However the percentage of women who gave birth after IVF or ICSI treatment who had a multiple birth has gradually decreased over time:

  • In 1992 for every 100 women who gave birth following IVF or ICSI treatment, 28 of them had a multiple birth (28%), that is, more than one baby.
  • By 2006 the proportion of multiple births had fallen, so that for every 100 women who gave birth following IVF or ICSI treatment 23 of them had a multiple birth (23%).

 

The proportion of women giving birth to singletons, twins and triplets following IVF or ICSI treatment, treatment cycles started in1992 to 2006

Graph showing the proportion of women giving birth to singletons, twins and triplets following IVF or ICSI treatment 1992-2006

Note: The figures given for ICSI treatment include those for SUZI cycles. What is SUZI?
Figures for live births refer to babies who were still alive at one month of age. They include singleton births and multiple births.

Note: Figures for triplets include those for triplets and higher order multiples.

The decline in the percentage of births that are multiple is due to a reduction in the number of embryos transferred in each cycle of treatment. From 1991 clinics in the UK were expected by the HFEA to transfer no more than three embryos in each cycle of treatment. Over the 1990s it became more common for clinics to transfer two embryos.

In 2001 the HFEA introduced a two-embryo transfer policy for women under the age of 40 years. In exceptional circumstances, three embryos were allowed to be transferred.

In 2004 this policy was revised so that now a maximum of two embryos can be transferred to women under the age of 40, with no exceptions to this rule. A maximum of three embryos can be transferred in women aged 40 and over.

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Are the chances of having a singleton or multiple birth different for IVF and ICSI treatment?

Since 1995 women who had ICSI treatment have been slightly more likely to have a multiple birth than women who had IVF.

The main difference in the outcome rates between ICSI and IVF is that a greater proportion of women have a singleton birth with ICSI. 

The single greatest health risk for women conceiving following fertility treatment is a multiple pregnancy.

The percentage of women undergoing IVF or ICSI treatment who gave birth to a singleton or multiples, treatment cycles started in 1992 to 2006

 

Singleton births:

Graph showing the percentage of women undergoing IVF or ICSI treatment who gave birth to a singleton 1992-2006

Multiple births:

Graph showing the percentage of women undergoing IVF or ICSI treatment who gave birth to multiples 1992-2006

Note: The figures given for ICSI treatment include those for SUZI cycles. What is SUZI?
Figures for live births refer to babies who were still alive at one month of age. They include singleton births and multiple births.

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Does the number of embryos transferred affect the birth rate (single embryo transfer)?

The single greatest health risk for women conceiving following fertility treatment is a multiple pregnancy. The risk of multiple births can be reduced by transferring fewer embryos.  

In 1992, 7 in every 100 women (7%) undergoing IVF or ICSI treatment where a single embryo was transferred gave birth to a singleton. The results were the same until 2003 when the number of women giving birth after single embryo transfer increased.

In 1992, 7 in every 100 women (7%) undergoing IVF or ICSI treatment where a single embryo was transferred gave birth to a singleton. The results were the same until 2003 when the number of women giving birth after single embryo transfer increased.

By 2006, 16 in every 100 women (16%) who had a single embryo transfer gave birth. This increase is probably due to an increasing use of ‘elective’ single embryo transfer (eSET).

Elective single embryo transfer

Elective single embryo transfer is where only one embryo is transferred during a cycle, even though the patient may have several embryos available.

A clinic will recommend elective single embryo transfer if they feel it is the best option for a patient, and if they are confident that their embryos are healthy and likely to implant. A single embryo is transferred when the risk of conceiving a multiple pregnancy following a two-embryo transfer is high. 

 

The percentage of women undergoing IVF or ICSI treatment who gave birth to a singleton or multiple following a single embryo transfer, treatment cycles started in 1992 to 2006

Graph showing the percentage of women undergoing IVF or ICSI who gave birth to a singleton or multiple following single embryo transfer 1992-2006

Note: The figures given for ICSI treatment include those for SUZI cycles. What is SUZI?
Figures for live births refer to babies who were still alive at one month of age. They include singleton births and multiple births.

Even when only a single embryo has been transferred, there is still a small possibility of a multiple birth. This can occur when the embryo that has been transferred divides and identical twins are produced.

Between 1992 and 2006, about 2 in every 1,000 successful single embryo transfers have resulted in a multiple pregnancy (0.2%).

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Does the number of embryos transferred affect the birth rate (two embryo transfer)?

The birth rates of both singletons and multiples following two embryo transfers have improved over time:

  • In 1992, 14 in every 100 women (14%) treated with assisted reproductive technologies (ART) involving a two embryo transfer gave birth to a singleton.
  • By 2006, 26 in every 100 women (26%) treated with a two embryo transfer gave birth to a singleton.
  • A two embryo transfer is three times more likely to result in a singleton than a multiple birth. Even so, the percentage of women who had a multiple birth following a two embryo transfer doubled between 1992 and 2006.
  • In 1992, 4 in every 100 women (4%) who had IVF and ICSI treatment involving a two embryo transfer had a multiple birth. By 2006, 8 in every 100 women (8%) had a multiple birth.

The single greatest health risk for women conceiving following fertility treatment is a multiple pregnancy. The risk of multiple births can be reduced by transferring fewer embryos.  

The percentage of women undergoing IVF or ICSI treatment who gave birth to a singleton or multiple following a two embryo transfer, treatment cycles started in 1992 to 2006

Graph showing the percentage of women undergoing IVF or ICSI treatment who gave birth to a singleton or multiple following a two embryo transfer 1992-2006

Note: The figures given for ICSI treatment include those for SUZI cycles. What is SUZI?
Figures for live births refer to babies who were still alive at one month of age. They include singleton births and multiple births.

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Does the number of embryos transferred affect the birth rate (three embryo transfer)?

The birth rate following a three embryo transfer remained relatively constant from 1992 until 2004:

  • In 1992, 15 in every 100 women (15%) who had IVF or ICSI treatment involving a three embryo transfer gave birth to a singleton. By 2003 this had increased to 18 women in every 100 (18%).
  • From 2004 the birth rate following a three embryo transfer reduced until by 2006, 13 in every 100 (13%) women treated gave birth to a singleton.

The single greatest health risk for women conceiving following fertility treatment is a multiple pregnancy. The risk of multiple births can be reduced by transferring fewer embryos.  

The percentage of women who had IVF or ICSI treatment who gave birth to a singleton or multiple following a three embryo transfer, treatment cycles started in 1992 to 2006:

Graph showing the percentage of women who had IVF or ICSI treatment who gave birth to a singleton or multiple following a three embryo transfer 1992-2006

Note: The figures given for ICSI treatment include those for SUZI cycles. What is SUZI?
Figures for live births refer to babies who were still alive at one month of age. They include singleton births and multiple births.

The reduction in the multiple birth rate is partly due to pressure within the sector and the HFEA two-embryo transfer policy, which was revised in 2004. The revised policy allows a maximum of two embryos to be transferred to women under the age of 40, with no exceptions to this rule. A maximum of three embryos can be transferred in women aged 40 and over.

As a consequence, from 2004 onwards the only women to have a three embryo transfer were women over the age of 40 years who fell into the poor prognosis category due to their age at treatment.

Over time, the percentage of women giving birth to multiples following a three-embryo transfer has decreased:

  • In 1992, 7 in every 100 women (7%) who had IVF or ICSI treatment where three embryos were transferred had a multiple birth. By 2003 this had decreased slightly to 5 in every 100 women (5%).
  • From 2003 onwards the number of women giving birth after a three embryo transfer reduced year on year until in 2006, 3 in every 100 women (3%) treated gave birth to multiples.

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What effect has the HFEA two-embryo transfer policy had on the rate of triplets and higher order multiples?

The single greatest health risk for women conceiving following fertility treatment is a multiple pregnancy. The risk of multiple births can be reduced by transferring fewer embryos.  

In 2001 the HFEA introduced a two-embryo transfer policy for women under the age of 40 years. In exceptional circumstances only, three embryos were allowed to be transferred.

In 2004 this policy was revised so that now a maximum of two embryos can be transferred to women under the age of 40, with no exceptions to this rule. A maximum of three embryos can be transferred in women aged 40 and over.

The main impact of the policy can be seen in the rate of triplets and higher order multiples born after IVF or ICSI treatment.

The percentage of women treated who had a triplet or higher order birth following IVF or ICSI treatment decreased over the 1990s. With the introduction of the two-embryo transfer policy in 2001, the decrease was much more rapid.

 

The percentage of women having IVF or ICSI treatment who had a triplet or higher order birth, treatment cycles started 1992 to 2006

Graph showing the percentage of women having IVF or ICSI treatment who had a triplet or higher order birth 1992-2006

Note: The figures given for ICSI treatment include those for SUZI cycles. What is SUZI?
Figures for live births refer to babies who were still alive at one month of age. They include singleton births and multiple births.

The impact of fertility treatment on the national rate of triplet births is illustrated in the following graph. Note that:

  • Following the widespread introduction of IVF, the triplet rate increased rapidly. Prior to the use of IVF, 1 woman in every 9,260 giving birth had triplets. This more than quadrupled to a peak of 1 in 2,130 in 1998.
  • Changes in clinical practice to reduce the number of IVF and ICSI cycles involving three-embryo transfers, and the introduction of the two-embryo transfer policy in 2001, have had a substantial impact on the triplet rate.
  • By 2007 the triplet rate was 1 in 4,975 which was just less than double the rate prior to the introduction of IVF.
    England and Wales national triplet rate per 10,000 women giving birth, 1938 to 2007

    Graph showing England and Wales national triplet rate per 10,000 women giving birth, 1938-2007

    Reference

    Birth Statistics. Review of the Registrar General on births and patterns of family building in England and Wales. Series FM1 nos.1 to 35 & historical series. London: Office for National Statistics.

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    Page last updated: 03 August 2012