Pre-implantation diagnostics have been carried out since the 1990s to detect chromosomal anomalies in embryos prior to implantation. Several techniques have been devised for this purpose.
Polar body biopsies were initially carried out prior to fertilisation. Polar bodies or globules are cells formed during egg maturation, which disappear after fertilisation. They should have the same number of chromosomes as the egg. Since the technique used to screen for chromosomal anomalies involving polar body biopsy is difficult, the method has “never become popular”.
Another procedure, namely embryo biopsy three days post-fertilisation, was widely used until the American Society for Reproductive Medicine declared it ineffective in 2008. Given the fact that interest in this technique persists (attributing failure to inadequate technologies), version 2.0 involving embryo biopsies at the blastocyst stage was developed without prior validation studies.
However, by postponing the biopsy—in this case three days post-fertilisation at the blastocyst stage—the number of false positives increases because the embryo itself corrects mutations which could appear during initial cell divisions. Version 2.0 therefore led to the destruction of a large number of embryos “in error“. The Preimplantation Genetic Diagnosis International Society found itself forced to publish new directives in 2016. But the latter impose totally arbitrary and insignificant limits for separating “normal embryos” from abnormal ones.
After two decades of use, which have not been clinically proven by pre-implantation screening, thousands of “normal” embryos have been eliminated, according to Doctor Norbert Gleicher, Medical Director of the Center for Human Reproduction in New York.
Bionews, Norbert Gleicher (11/12/2017)