About 10 years ago, Levent Keskintepe PhD and I introduced Comparative Genomic Hybridization (CGH) into the clinical IVF arena, as a preimplantation genetic sampling (PGS) method that enables full karyotyping (numerically chromosomal analysis) of all 23 pairs of an embryo’s chromosomes so mas to determine its subsequent ability to propagate a viable pregnancy (i.e. its “competence”). Since then we have, over a period of a decade, authored many articles on the clinical utility and advantages associated with the selective performance of embryo PGS and with it have witnessed embryo karyotyping emerge as a valuable efficiency tool in the IVF arena. Several alternatives to CGH have since emerged and while none are perfect, they have all enhanced our ability to better select the most “competent embryos for transfer to the uterus, thereby improving the efficiency of IVF, and reducing the risk of chromosomal miscarriages and birth defects. One recently introduced method known as “Next Generation Gene Sequencing (NGS)” bears special mention since its improved accuracy and reliability over previously used methodologies, has established it as a method of choice when it comes to embryo karyotyping..
Gene Sequencing is a method that determines the precise order of nucleotides within a DNA molecule. The method/ technology determines the order of the four bases—adenine, guanine, cytosine, and thymine—in a strand of DNA. A new generation of sequencing technologies known as NGS now provides unprecedented opportunities for high-throughput functional genomic research. NGS is currently being applied to identify the karyotype of the human embryo and in my opinion is more reliable than other available PGS methodologies.
NGS can be conducted reliably on blastomeres, removed from the trophectoderm of day 5-6 blastocysts. In my opinion, day 7-blastocysts so rarely will propagate viable pregnancies, as to render them ineligible for PGS biopsy.
Based upon available data, it is my opinion that the time has arrived to recommend that blastocyst NGS be used as the preferred method for PGS in IVF.