HELSINKI – Mitochondrial DNA level appears to be a useful biomarker for in vitro fertilization embryo viability, according to findings from a blinded prospective non-selection study.
An analysis of 280 chromosomally normal blastocysts showed that 15 (5.4%) contained unusually high levels of mitochondrial DNA (mtDNA) and the remaining blastocysts had normal or low mtDNA levels. Of 111 of the blastocyst transfers for which outcome data were available, 78 (70%) led to ongoing pregnancies, and all of those involved blastocysts with normal or low mtDNA levels, while 8 of the 33 blastocysts that failed to implant (24%) had unusually high mtDNA levels, Elpida Fragouli, PhD, reported at the annual meeting of the European Society of Human Reproduction and Embryology.
Thus, the ongoing pregnancy rate for morphologically good, euploid blastocysts was 76% for those with normal/low mtDNA levels, compared with 0% for those with elevated mtDNA levels – a highly statistically significant difference. The overall pregnancy rate was 70%, said Dr. Fragouli of Reprogenetics UK and the University of Oxford.
The blastocysts in the study were generated by 143 couples who underwent IVF in a single clinic. All blastocysts were biopsied and shown to be chromosomally normal using preimplantation genetic screening.
“The study demonstrates that mitochondrial DNA levels are highly predictive of an embryo’s implantation potential,” Dr. Fragouli said, noting that the “very robust” findings could potentially enhance embryo selection and improve IVF outcomes.
The methodology used in the study has been extensively validated, she said. However, a randomized clinical trial will be necessary to determine the true extent of any clinical benefit, she added, noting that research is also needed to improve understanding of the biology of mtDNA expansion.
The findings are of particular interest, because while it is well known that chromosomal abnormality in embryos is common and increases with age, and is the main cause of implantation failure, it has been less clear why about a third of euploid embryos fail to produce a pregnancy.
“The combination of chromosome analysis and mitochondrial assessment may now represent the most accurate and predictive measure of embryo viability with great potential for improving IVF outcome,” according to an ESHRE press release on the findings.
Levels of mtDNA can be quickly measured using polymerase chain reaction. Next generation sequencing can also be used, Dr. Fragouli noted. However, since aneuploidy remains the most common cause of embryo implantation failure, mtDNA and chromosome testing would be necessary.
“Mitochondrial analysis does not replace [aneuploidy screening]. It is the combination of the two methods ... that is so powerful,” she said, noting that efforts are underway to develop an approach to assessing chromosome content and mtDNA simultaneously to reduce the extra cost.
The group has started offering mtDNA quantification clinically in the United States and has applied to the Human Fertilisation and Embryology Authority for a license to use the testing in the United Kingdom.
Reprogenetics provided funding for this study.