This summer, we are introducing a new procedure in our laboratory that will allow us to do genetic testing on embryos that have reached the blastocyst stage of development. Traditionally, embryos are biopsied when they are just 3 days old at which time they should have reached the 8-cell stage (see figure 1). The biopsied cell is sent to the genetics laboratory for testing while the remainder of the embryo continues to grow in our laboratory. The genetic testing results are received 48 hours later, when we hope that the embryo will have reached the blastocyst stage (see figure 2). Blastocysts that have passed genetic screening can be transferred or frozen for later use.
Performing the biopsy when the embryo has become a blastocyst is more technically challenging, and it allows less time for the genetics lab to do their testing. However, in a blastocyst, we are specifically able to biopsy from the part of the embryo that will become the placenta, and we can get more than 1 cell, which allows for greater accuracy in the genetic testing. Depending on how quickly the test is run, the embryo may have to be frozen while we wait for the results.
While freezing is inconvenient, it does allow time for more complex genetic testing, and for multiple tests if necessary. And, with the success of vitrification for preserving embryos (see Fertility Flash Vol. 7, Issue 3), we are confident that the frozen embryos will survive and implant at high rates when thawed.
In the next few years, we expect that the traditional methods for biopsy and genetic testing will disappear and that blastocyst biopsy will be the standard procedure. As genetic testing evolves, it will not be possible to rely on just a single cell from an embryo to get dependable results. We already know that there is genetic variability among cells in an individual embryo, a phenomenon known as mosaicism, and our new procedure will overcome this problem.
In the coming months, we will announce an exciting new partnership with a Bay Area genetic testing lab, and we will keep readers informed on our progress with genetic testing in embryos. This is an exciting field that continues to evolve.