Single Embryo Transfer increases pregnancy rates, reduces risks

Reported in BioNews (March 2008) by Rebecca Robey

Scientists at a UK fertility clinic have reported that a new IVF technique may increase the rate of pregnancy while 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 percent 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.

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.
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