Chromosome screening may increase IVF success in older mothers
Progress Educational Trust03 November 2012
Using a new IVF technique could considerably increase older women's chances of pregnancy, a small clinical trial presented at a fertility conference suggests.
In the technique embryos produced via IVF are first tested for major genetic abnormalities using a method called comprehensive chromosomal screening (CCS). For this, samples are taken from embryos at the blastocyst stage, when they have around 100 cells.
CCS tests whether embryos have the normal 46 chromosomes, 23 from each parent. The genetically normal embryos are cryopreserved for a month or two before being thawed and inserted in the womb. The cryopreservation period is thought to allow the woman’s hormones to settle after the disturbance caused by IVF drug treatment.
A randomised controlled trial in 60 patients compared the new technique against standard embryo screening, where embryo quality is assessed primarily by evaluating their appearance under a microscope.
The study was presented at a meeting of the American Society for Reproductive Medicine (ASRM) in San Diego, USA. Although the abstract relating the findings is unclear, the Telegraph says that the CCS technique 'took the successful pregnancy rate in a group of 38 to 42-year-olds from 33 to 61 percent'.
The researchers also reported that none of the women implanted with embryos that had been through CCS had first trimester miscarriages, whereas six of the 30 women implanted with embryos that had been through standard screening did miscarry within the first trimester.
Talking to the Telegraph, study co-author Dr Mandy Katz-Jaffe from the Colorado Centre for Reproductive Medicine, said: 'What we've been able to show is that a woman aged 38 to 42, if she has a blastocyst with a normal number of chromosomes, her chances of implantation are independent of her age. So she has the same chances of implantation – at 60 percent – as a woman who is 32'.
The risk of producing an embryo possessing an abnormal number of chromosomes (a condition known as aneuploidy) increases as a woman ages. By the age of 40, 75 percent of a woman's embryos are aneuploid, and this heightens the risk of any resulting child having disorders like Down's syndrome and also increases the risk of miscarriage.
The Telegraph reports that 'clinics in the USA, Australia and Spain are hurrying to adopt the techniques but in Britain only a tiny fraction of IVF patients is benefiting'.
Speaking to the newspaper, Dr Dagan Wells, a geneticist who helped pioneer embryo screening, and who was not involved in this study, said that if the results were confirmed, standard IVF practices in the UK would have to be 'completely re-evaluated'.
'I think the evidence is starting to mount up that chromosome screening may be ready for prime time', he added. 'CCS could potentially represent a revolution in the way IVF is done and infertility is treated'.
However, Mr Stuart Lavery, a consultant gynaecologist at the Hammersmith Hospital in London, told the Daily Mail that CCS is 'controversial. To put an embryo through the freeze and a thaw is a bit of an insult. It's a shock, and sometimes it will kill a few cells'.
Dr Linda Giudice, president-elect of the ASRM, said that the next step in assessing the new technique 'will be large scale trials including data from birth outcomes'.
Reproduced with permission from BioNews, an email and online sources of news, information and comment on assisted reproduction and genetics.