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HELSINKI -- Embryos with higher levels of mitochondrial DNA may be less likely to lead to a pregnancy during an IVF cycle, a small prospective study presented here found.

Of all the embryos with normal or low levels of mitochondrial DNA, 76% implanted successfully and led to an ongoing pregnancy compared with 0% of embryos with elevated mitochondrial DNA levels (P<0.0001), reported , of Reprogenetics in Oxford, England, and colleagues.

"Only one-third of IVF cycles result in a pregnancy, and part of the reason for this is we're not very good at determining which of the embryos produced has the highest chance of making a baby," said Fragouli in an interview. "So, our method seeks to help reveal the embryo most likely to be viable."

Examining mitochondrial DNA as a biomarker to evaluate embryo viability is not entirely new -- having previously been validated in a retrospective analysis of 700 blastocysts in Europe and the U.S. But the authors note that no prospective studies have been undertaken to confirm this possibility.

This prospective, blinded study with a nonselection design at the annual meeting.

Fragouli's team found that overall, 70% of the 110 euploid embryos (those with the proper amount of chromosomes) implanted led to ongoing pregnancies, and all of them (100%) had lower or normal levels of mitochondrial DNA. Of the 30% of the embryos that failed to implant, 24% had higher levels of mitochondrial DNA.

The authors compared only mitochondrial DNA levels in embryos to IVF outcomes, so the results were not subject to bias. They biopsied 280 blastocysts (embryos that had been cultured for 5 to 6 days), but the outcomes of only 111 of these embryos were known. Embryos were taken from 143 couples at the same IVF clinic, with mean maternal age of 37.2 years. An initial examination of all 280 blastocysts revealed elevated mitochondrial DNA levels in 15 (5.4%).

The authors note that randomized clinical trials are needed to determine the true extent of any clinical benefits, as well as additional research into the biology of mitochondrial DNA itself.

Fragouli said that she views mitochondrial DNA screening as a supplement to the chromosome screening method (which identifies embryos with the wrong number of chromosomes, or aneuploidy). She added that this test would only be carried out if a provider had identified at least four chromosomally normal embryos for a patient.

"Having an accurate test of embryo viability means we could select the one with the highest implantation potential," said Fragouli. "This would enable doctors to make a more accurate assessment of embryos and which one to transfer to the uterus to lead to an ongoing pregnancy."

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