Volume 108, Issue 2, Pages 228–230
Richard J. Paulson, M.D.
In the current practice of in vitro fertilization (IVF), preimplantation genetic screening (PGS) is increasingly used to select embryos for transfer. This strategy is designed to maximize the probability of embryo implantation by eliminating embryos with low implantation potential from the cohort. However, PGS is inherently imperfect. Errors may occur during the genetic analysis of the small amount of DNA collected. More importantly, mitotic mosaicism, whose precise incidence in the preimplantation embryo is not known, may lead to sampling errors due to the intentionally limited collection of cells in the trophectoderm biopsy. In this manner, abnormal cells may be collected in an otherwise euploid embryo and vice versa. Therefore, it is inevitable that some normal embryos will be discarded, leading to an overall decrease in the cumulative pregnancy rate achievable by the eventual transfer of all embryos in the cohort.