on of human embryos used low resolution techniques on embryos derived from couples with fertility problems who are at risk for embryonic aneuploidy, an aberrant number of chromosomes, such as three copies of chromosome 21 that results in Down's syndrome. Therefore, little was known about the frequency and type of chromosomal imbalances in embryos from normal, fertile women," said Ms Vanneste. "Our new technique has enabled us to show that chromosomal abnormalities are far more common and complex than previously anticipated, even in embryos from young, normal fertile couples. This leads us to believe that such abnormalities must be present in all human IVF-ICSI embryos.
"Although in vitro culture conditions are known to have a limited influence on the rate of chromosomal imbalances in IVF/ICSI embryos, it is probable that the chromosome instability observed in vitro also occurs in spontaneous pregnancies since, at most, 30% of human conceptions result in a live birth and more than 50% of spontaneous abortions carry chromosomal aberrations. The high rate of chromosomal abnormalities is almost certainly responsible for the low fecundity of humans compared with other mammals," she added.
The scientists say that their work has important implications for preimplantation genetic screening (PGS) in fertility treatment. PGS is routinely used in many fertility centres for couples who encounter problems with conception, particularly for advanced maternal age, repeated failure of implantation, repeated miscarriages, or severe male fertility problems. In PGS, a single cell is removed from the early embryo for genetic testing, since it is hypothesised that the selection of chromosomally normal embryos for uterine transfer would increase the live birth rate and decrease the spontaneous abortion rate per embryo transferred.
"Although PGS is promoted as a way of increasing the chances of a successful pregnancy," said Ms Vanneste, "there has never been any
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