Chromosomes in early human embryo development: Incidence of chromosomal abnormalities, underlying mechanisms and consequences for development

Introduction Reproduction in humans is considered to be a relatively inefficient process, as the chance of achieving a spontaneous pregnancy after timed intercourse is only approximately 30%. This is much lower than the 70-90% estimated for other species such as the rhesus monkey, the captive baboon, or rodents and rabbits. The inefficiency of human reproduction is mainly explained by the high incidence of preclinical losses, an estimated 60% of all conceptions. Early pregnancy loss is mainly explained due to the occurrence of chromosome abnormalities, which have been identified in the majority of spontaneous abortion samples investigated. The introduction of assisted reproductive technology (ART) and specifically in vitro fertilization (IVF) has allowed better insight into human early embryo development and it has become clear that chromosomal abnormalities identified in abortion material from in vivo conceptions are also frequently identified in preimplantation embryos generated by IVF. This indicates that chromosome instability is an inherent feature of human conceptions. So far, advanced maternal age remains the only etiological risk factor identified for chromosomal aneuploidy [1]. However, increasing evidence has made it clear that most preimplantation embryos do not have a uniform chromosomal constitution in all cells and are said to be mosaic as a result of post-meiotic errors in chromosome segregation. The mechanisms underlying this phenomenon and its consequences for developmental potential of the preimplantation embryo are still poorly understood.

• View at Publisher
• View at Scopus