A test that checks for abnormal amounts of DNA in IVF embryos has raised pregnancy rates at US fertility clinics that have started to offer the procedure.

Scientists in Oxford who helped develop the test claim it can boost the chances of an IVF pregnancy by 10 percentage points, leading to success rates of about 75% in 35-year-old women.

The test does not improve the quality of IVF embryos created at fertility clinics, but gives doctors a new way to identify the healthiest and most likely to produce a pregnancy.

Many IVF clinics already offer a procedure called pre-implantation genetic screening, or PGS, which is used to spot embryos that have the wrong number of chromosomes, the structures that carry the human genetic material.

Chromosome abnormalities are the single greatest cause of embryos failing to implant or miscarrying. But even with PGS, which costs from £2000 to £3000 in Britain, about a third of embryos do not go on to produce a successful pregnancy.

Researchers at the NIHR Oxford Biomedical Research Centre and genetics laboratory Reprogenetics in the US, noticed that many of the embryos that failed to implant after PGS had abnormally high levels of DNA from structures called mitochondria. Healthy cells often carry hundreds of mitochondria to provide them with energy.

“Based on our findings we have devised a test whereby a small number of cells, carefully removed from an embryo, can be measured for the amount of mitochondrial DNA present,” said Elpida Fragouli, who led the research at Reprogenetics. “This will help guide doctors to the IVF embryos with the greatest chance of producing a viable pregnancy.”

Several clinics in the US, including the New York University Fertility Center, have already begun to offer the test, called MitoGrade. Data from the first 100 couples suggest the test boosts pregnancy rates from about 65% to 75%, according to a presentation to be given at the American Society for Reproductive Medicine annual meeting in Baltimore on Tuesday.

“Anything that reduces the number of unsuccessful embryo transfers that patients have to endure will certainly be welcome. This important discovery indicates that mitochondria represent an important piece in the complex jigsaw puzzle that is infertility,” said Dagan Wells, who leads the UK arm of the project.

Scientists are not sure why some embryos experience a sudden rise in mitochondrial DNA, or how this affects their ability to implant. One possibility is that defective embryos make more mitochondria to give them enough energy to survive, but ultimately fail and stop growing.

“These tests don’t make the embryos any better than they were in the beginning. There will still be patients out there, and many of them, who don’t produce any viable embryos at all. So it’s not going to guarantee future pregnancy rates to every patient overnight, but it will help,” Wells said.
The research team is in the process of applying to the UK fertility regulator, the Human Fertilisation and Embryology Authority, for a licence to offer the procedure in Britain. Should they gain approval, the test could be offered in addition to PGS for an extra £200 from next year.

“There is a lot of interest in mitochondrial activity within eggs and developing embryos and this study presents a fascinating insight into the potential relationship between mitochondrial activity in genetically normal embryos and their potential for developing into a viable pregnancy,” said Adam Balen, consultant in reproductive medicine at Leeds Teaching Hospitals NHS Trust and chair of The British Fertility Society.

“It is still early days and the proposed test requires much more work and validation before application into clinical practice. There is no doubt this is a very important line of research and Dr Wells and his team are to be congratulated for what they have achieved to date.”