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Single embryo transfer increases pregnancy rates, reduces risks

26 February 2008
Appeared in BioNews 446

Scientists at a UK fertility clinic have reported that a new IVF technique may increase the rate of pregnancy whilst decreasing the risk of multiple births. The study, published in the British Journal of Obstetrics and Gynaecology, involved nearly 2500 women over a three-year period and found that implanting a single, more mature embryo improved the chance of a successful pregnancy.

The new technique involves allowing the fertilised egg to grow longer in the laboratory before it is implanted - five days rather than the usual two or three. At this stage the embryo has developed into what is called a blastocyst, and this enables clinicians to select blastocysts that are growing well and are therefore more likely to implant successfully. One will be implanted, the others may be frozen for future use. The study, led by Dr Yakoub Khalaf at the Assisted Conception Unit at Guy's and Saint Thomas's Hospital, compared pregnancy rates of two groups of women. The first were treated between July 2004 and December 2005 using only conventional techniques. The second were treated between January 2006 and July 2007 and were either treated conventionally or offered the single embryo transfer technique if they were felt to be at risk of multiple pregnancy (generally this is women under 35). In the first group, the pregnancy rate was 27 per cent and the multiple pregnancy rate was 32 per cent. In the second group, the pregnancy rate rose to 32 per cent and the multiple pregnancy rate decreased to 17 per cent.

The findings are timely, announced amidst growing concerns of the increasing burden of multiple births on the NHS, a trend believed to be driven by IVF. One in four IVF births are twins or triplets, compared to one in 80 naturally-conceived births. This is because more than 90 per cent of IVF treatments performed in Britain implant two or more embryos in an attempt to maximise the chance of pregnancy. Couples are naturally anxious to optimise this chance and may even see twins as an 'instant family', bypassing the need for future courses of IVF. However, multiple pregnancies carry many increased risks to both mothers and babies, including pre-eclampsia, premature birth, mother and infant mortality and long-term disabilities such as cerebral palsy. This carries a huge emotional cost for the families, and a significant financial cost for the NHS. According to a BBC News Online report, last year neo-natal beds in the UK were filled to capacity for the first time, illustrating the gravity of the situation.

Dr Khalaf said: 'we believe firmly that a twin pregnancy is not an ideal outcome...the risks are real and we see the heartache time after time'. Single embryo transfer is currently available in some clinics, but the Human Fertilisation and Embryology Authority are encouraging clinics to make it common-place for suitable couples.

SOURCES & REFERENCES
IVF technique 'cuts twin births'
BBC News Online |  21 February 2008
New IVF technique: greater success rate, fewer multiple births
The Independent |  21 February 2008
One embryo at a time 'makes IVF less risky'
The Daily Telegraph |  21 February 2008
Selective Single Embryo Transfer Of A Blastocyst For IVF Increases Pregnancy Rate And Lowers Twin Births
Medical News Today |  22 February 2008
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