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The first live births following PGD were reported in London in 1989. Two sets of twin girls were born to five couples at risk of passing on an X-linked disorder. About 90% of abnormal embryos can now be detected using PGD techniques. Not all chromosomal or genetic abnormalities can be determined with these procedures, since only a restricted number of chromosomes can be diagnosed at one time during the course of a single procedure. Numerous animal studies and some human studies show that the microsurgery of the embryo (biopsy) needed to remove the cells does not affect the normal development of the baby. This procedure, however, has only been performed in less than 500 patients worldwide, therefore, the precise negative effects, if any, are unknown. Even though there have been more than 200 live births after PGD for aneuploidy world-wide to date (May 2001), this procedure is still relatively new. In animal studies there have been no apparent problems and preliminary evidence with human embryos suggests that this is also true. In a study at the University College of London, researchers recently examined 12 preimplantation embryos with a new technique that combines whole genome amplification (WGA) and comparative geomic hybridization (CGH). Results were that 8 in 12 embryos studied were found to have significant chromosomal abnormalities. This may explain why humans have, at best, a 25% chance of achieving a viable pregnancy per month.
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