Preimplantation Genetic Screening For All? Is It Wrong To Do Genetic Testing On All IVF Embryos?

Microscope Stage with Micromanipulators
Copyright J. Pabon collection

Preimplantation Genetic Screening

Preimplantation genetic screening refers to the test that evaluates embryos for the presence of the normal number of chromosomes. Preimplantation genetic diagnosis refers to the testing of embryos for the presence of a known disease that is carried by the family. Whether clinics should offer PGS to all IVF patients is a very good question. The answer to that question has changed recently. In the past, the past being early 2012, we were still testing our embryos on the third day of “in vitro” growth. We had been doing embryo biopsies for the past 12 years and offering the highest technology available. All of our patients understood that the biopsy of day 3 embryos had the significant limitation of “mosaicism.” That is, there was a 7-10% chance that the single cell that was tested would not represent the “inner cell mass” that would develop into the baby.

A cell or blastomere being removed from a day 3 embryo
Copyright: J. Pabon collection

Recently, after more scientific information became available and the techniques for the biopsies of blastocysts were improved, we realized that the biopsy of blastocysts would be less invasive to the embryo than a day 3 biopsy and that the reading of more than one cell would provide our reference labs with more DNA for testing and therefore a higher veracity of the results. Dr. Pabon met with Dr. Hughes from Genesis Genetics during a congress in Austin, Texas in May 2012. At that meeting, Dr. Hughes shared much recent information regarding increased accuracy of pre-implantation genetic screening and diagnosis when several trophectoderm cells were submitted for analysis. It is estimated that the results of trophectoderm biopsies are more than 98% accurate.

Laser Assisted Hatching
Copyright J. Pabon collection

The accuracy of the genetic tests of embryos based on the biopsy of the trophectoderm are demonstrated by the pregnancy rate in excess of 80% when a single embryo tested in this way is implanted. By comparison, embryos that were biopsied on the third day, did not have as high an implantation rate. This most likely was due to limitations due to mosaic embryos, but also may have been due to the actual biopsy process of a day three embryo.

A hatching blastocyst just prior to laser biopsy
copyright J. Pabon Collection

So, if a physician can transfer a single embryo and enjoy a chance of pregnancy in excess of 80%, this means that the technology is more accurate than before and also that there is no need to transfer more than one embryo. That means that blastocyst biopsies may revolutionize IVF by allowing more single embryo transfers with a very high chance of pregnancy.

The table below shows typical results of trophectoderm blastocyst biopsies. “Euploid” is a genetic term that refers to the normal number of chromosomes. The X and Y chromosomes indicate the gender of the embryo as XX female or XY male.