Wednesday 24 October 2007
Since the birth of the first baby achieved through conception outside of the human body in 1978, the principles of "in vitro" fertilization and culture have remained the same - careful establishment and maintenance of a well-controlled, sterile environment in which the normal physiology of fertilization and early development can be played out relatively undisturbed to provide healthy embryos for transfer back into the body. During the ensuing two decades, much has been learned, however, about the tolerances of such a system and how this technique can be exploited to treat a widening range of infertility cases. There have been great strides made in development of more appropriate culture media that has enabled embryos to be grown for extended periods of time in culture. Surplus embryos and possibly eggs may now routinely be cryopreserved in liquid nitrogen for use in subsequent attempts at pregnancy. Fertilization itself is no longer a hit-and-miss affair with the advent of assisted fertilization through micromanipulation. Embryos can be micro-manipulated for cell biopsy to determine their genetic status as well as aid in their ability to implant through drilling into their outer shell (assisted hatching). Embryo Biopsy is performed for preimplantation genetic diagnosis (PGD) and enables the screening of both the unfertilized egg by removal of the first polar body, or the fertilized multi-cellular embryo by removal of one or more cells either at the 6-12 cell stage(see picture) or from the trophectoderm of the blastocyst. This material can be probed for both genetic mutations or gross chromosomal errors. This technology remains in its infancy and can be of profound importance clinically, but at this time only for cases with very clear medically-defined needs. The biopsy procedure requires very exacting skills of the IVF laboratory, and the egg or embryo is not entirely free of risk during the procedure. Hence, couples whose offspring have a high chance of inheriting a genetic disorder may have their embryos screened. Women who are at risk of generating eggs with a high risk of chromosomal anomalies can benefit from having their eggs or embryos screened for chromosomal normality.