Looking to the future: developments in preimplantation genetic diagnosis

Since the first clinical preimplantation genetic diagnosis (PGD) cycles carried out in 1989, continuous technical improvements have supported progression from what was initially perceived to be an experimental procedure to a widely acceptable alternative to conventional prenatal diagnosis. PGD requires the use of assisted reproductive technology (ART) to create the preimplantation-stage embryo, followed by biopsy to obtain cell(s) for genetic analysis and, finally, transfer of selected embryos to the womb to establish a pregnancy. PGD is an important reproductive option for parents at high risk of transmitting a single-gene or specific chromosomal abnormality to their children (high-risk PGD), supporting the establishment of a healthy pregnancy while precluding possible pregnancy termination. Alternatively, embryos may be tested for ploidy status, a test widely known as preimplantation genetic screening (PGS). PGS is considered to be a lowrisk form of PGD, offered to women of advanced maternal age or couples with poor reproductive history, which aims to select euploid embryos for transfer to improve the implantation and live birth rates after ART. However, low-risk PGD is controversial and constitutes one of the most highly debated topics in reproductive medicine over the last decade, chiefly because it was introduced into routine clinical practice before its clinical benefit was clarified. Reports to date evaluating ART outcomes following PGS have shown contradicting evidence, mainly complicated by the numerous parameters involved in PGS procedures, many of which may introduce bias. It is paramount to resolve this issue and the only way is through large multicenter randomized controlled studies, such as one currently being organized with the support of the European Society of Human Reproduction and Embryology (ESHRE) [1].