IVF experts divided over mosaic embryos

6 de maio de 2016

Debate is intensifying among fertility specialists about the use of mosaic embryos in IVF.  
Mosaic embryos – embryos that are characterized by irregular numbers or arrangements of chromosomes in some cells – have typically not been used by fertility specialists (at least in the US) due the likelihood that any resulting foetus will suffer from genetic disorders.
Yet some experts believe the embryos are safer than popular opinion suggests; others are going as far as to advocate the routine use of mosaic embryos in IVF clinics.
One reproductive medicine expert recently claimed that preimplantation genetic screening processes used to detect abnormal embryos are inaccurate and that many of what are known as ‘mosaic embryos’ are actually gametes that will lead to healthy babies.
Dr. Norbert Gleicher, the director of the Center for Human Reproduction in New York, recently tested PGS by tranferring seemingly abnormal embryos into women seeking IVF. Gleicher has reported four normal pregnancies since he began his test.
“I think the biological hypothesis that you can, from a single biopsy, determine whether an embryo is normal or chromosomally abnormal — that is flawed,” he recently told the New York Times.
Gleicher’s view is controversial, with many PGS specialists arguing that new diagnosis techniques allow for very low rates of false-negative readings.
Three researchers from the world’s largest genetics laboratory, Reprogenetics, recently published a paper in the journal Fertility and Sterility arguing against Gleicher’s view. The paper ostensibly shows clinical value of HR-NGS for detecting mosaicism and as a selection tool to assist in identifying embryos with the greatest likelihood of viability; the authors also claim to have established that mosaic embryos can be considered a distinct category in terms of viability.
“Previous embryo selection methods had limited possibility of detecting mosaic embryos”, said the lead author of the article, Santiago Munne. “Now…we can detect mosaic embryos, which miscarry more frequently and implant less frequently, allowing the most viable embryos to be prioritized for transfer”. 
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