Baby Problems – UK Urged To Adopt New DNA Screening For IVF Embryos
A new technique to genetically screen IVF embryos should be considered for use in the UK, fertility experts say. The call comes after research revealed it could help doctors select embryos that have the best of chance of leading to a pregnancy. Pre-implantation genetic screening (PGS) is more common in the US than the UK, and is used by doctors to flag up embryos with an abnormal number of chromosomes – the main reason why embryos fail to implant in the womb.
But other factors also affect whether an embryo will implant: around a third of embryos with the correct number of chromosomes also fail to lead to a pregnancy when transferred to the womb. Intriguingly, scientists have recently found that many of these apparently healthy embryos have something in common: they have increased levels of the DNA that is found within mitochondria – the tiny energy-generating structures that sit inside cells. The discovery, scientists say, offers a new tool for genetically screening embryos with the technique, known as mitochondrial DNA quantification, recently made available in the US.
Now fertility experts are calling for the technique to
be considered for approval in the UK. “It is looking promising and I think that we would certainly like to discuss it with our patients as an option for them,” said Stuart Lavery, consultant gynaecologist and director of IVF Hammersmith at Hammersmith hospital.Lavery says the call is supported by new research by scientists led by Elpida Fragouli at the University of Oxford. The research suggests screening embryos for their levels of mitochondrial DNA could help doctors select those that are most likely to survive and thrive in the womb.
Presented at the annual meeting of the European Society of Human Reproduction and Embryology, in Helsinki, the research involved the study of 280 five to six-day-old embryos, all of which had the correct number of chromosomes. The embryos were produced from 143 couples, with the average age of the women reported as 37.2 years.
While the team measured the levels of mitochondrial DNA for these embryos, they did not reveal the results until after the embryos were transferred into the womb. “We transferred embryos and then went back and said, ‘how good is this test?’” said Jamie Grifo, a co-author of the research from NYU Langone Fertility Center.
The team found that of the 111 embryos, for which data is available, 70% implanted in the womb, while 30% failed to do so. While all of those that successfully implanted were found to have normalor low levels of mitochondrial DNA, more than a fifth of those that failed to implant had unusually high levels of mitochondrial DNA.
That, the scientists say, suggests that screening embryos for their levels of mitochondrial DNA could improve the selection of the embryo to be transferred into the womb during IVF, while reducing the need to transfer multiple embryos. Embryos that are not transferred are frozen.
“Embryos [that] have an amount of mitochondrial DNA above this threshold value, they just don’t implant. So it is highly diagnostic in that way,” said Dagan Wells of the Nuffield department of Obstetrics and Gynaecology at the University of Oxford, another author of the research. It is not known why embryos with high levels of mitochondrial DNA rarely implant in the womb, but one possibility is that it is a sign that the embryo has problems with its mitochondria, or that it is attempting to produce more energy to overcome other problems.
Screening an embryo to check the number of chromosomes can be expensive, with PGS typically costing between £2,000 and £3,000 in the UK. But, says Wells, testing for levels of mitochondrial DNA can be carried out in tandem, making it a low-cost additional process.
But while genetic screening could help with embryo selection, Wells adds, it does not allow scientists to overcome problems with the embryos themselves. “It is important to emphasise that these tests, the chromosome tests, the mitochondrial DNA [test], none of them make the embryos any better than they were to begin with,” he said.
The new technique has recently been made available in the US, and Lavery and his team are asking the Human Fertilisation & Embryology Authority (HFEA) to consider approving the technique for use in the UK.
A spokesperson for the HFEA said, “Our Scientific and Clinical Advances Advisory Committee is considering data that has been presented to it in relation to mitochondrial DNA quantification, and will be publishing its advice in due course.”
