Molecular, morphological, and kinetic diagnosis of human preimplantation embryo viability

There have been phenomenal advances in the field of reproductive medicine and success rates following in vitro fertilisation have improved dramatically in recent years. The aim of this project was to improve our understanding of human preimplantation embryo development by identifying potential markers of viability that may aid us in selecting the best embryo for uterine transfer in the clinical embryology laboratory. Investigations into the distribution of cytoskeletal F-actin in human embryos demonstrated that a highly organised actin cortex is important for embryo cleavage and continued development to the blastocyst stage. Whilst they are polarised in the mouse from the oocyte to the blastocyst, the regulatory proteins leptin and STAT3 are co-localised only at the oocyte stage in humans, and are distributed within different cytoplasmic domains in human cleavage stage embryos and blastocysts. Whether polarity in humans is predetermined in the oocyte remains elusive, but none of the evidence generated in this thesis supports this idea. Leptin transiently activates STAT3 via the long form of the leptin receptor, and most significantly in the ICM of human day 6 blastocysts. Morphological features of blastocysts that can be visualised microscopically, such as a double ICM and cytoplasmic projections connecting the ICM to the TE, provide clues to their viability and may help us to choose the most suitable embryo from a cohort when deciding which to transfer. Nuclear volumes may in future contribute to this selection. Using time lapse technology to study cleavage patterns is now a routine occurrence in the clinical embryology laboratory. The results in this thesis show that distinctive patterns of divisions and the site at which blastocysts hatch can provide us with more information than a snap-shot morphological evaluation. Finally, contributing to the development of modelling software and predictive algorithms for the study of human embryos, particularly in time lapse imaging, means that our understanding of this fascinating area of medicine will continue to progress