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Preimplantation Genetic Screening: Technical Problems With Original PGS

The Center for Human Reproduction’s Dr. David H. Barad explains the technical problems with the early versions of Preimplantation Genetic Screening (PGS) that led to false positives and lower pregnancy rates.

This has been around in several different forms over time. Originally the screening was done on cleavage stage embryos, using a technique that involved staining a few of the chromosomes and looking at them with fluorescence microscopes. There were technical problems with that process that made it hard to actually read how many chromosomes there were. As a result there were several papers published that showed doing the PTS didn’t improve the pregnancy outcome. So the promise was there (the theoretical promise was there) picking out that perfect embryo, but in fact it didn’t work out when people looked at it empirically. The pregnancy rates were lower in people who were biopsied. The issue at that time was that perhaps biopsying a cleavage stage embryo (which meant pulling one cell away) at that point was 12 percent of the volume of the embryo, so you are taking a big piece of the embryo away. Technical problems in doing the testing itself also contributed to wrong diagnosis and possible damage to the embryo.