| Summary: | This thesis describes the development of a novel system to grade the ‘difficulty’ of an embryo transfer (ET) procedure. A systematic review of the prevalence of ‘difficult’ ET has revealed marked heterogeneity across the literature with no real consensus ‘definition’ or ‘grading system’ available for clinicians to use. A new systematic approach to grading ET procedures has been proposed and tested. It has the ablity to predict IVF outcomes accurately and has proven to be reliable. The ‘difficult’ ET procedure has been shown in this thesis to be detrimental to IVF outcomes when a fresh single blastocyst is transferred. All embryos of different qualities are affected to some degree by a difficult ET, but it appears that high quality blastocysts are proportionally more affected than the lower quality embryos, which have a lower potential to implant, though the mechanism is not clear. The embryo transfer time (ETT) is fundamental in determining the implantation potential of a single blastocyst. Once the ET procedures takes longer than ‘120-seconds’ and ETT is prolonged, there is a significant impact on both pregnancy and clinical pregnancy rates. The detrimental impact of increasing ETT on pregnancy rates was found to be independent of an embryo’s quality. The ETT appears to be a more accurate way to predict IVF outcomes than a stratified grading scale, though combining a descriptive scale with ETT may offer the optimum grading system. This thesis has shown that embryo cooling during ET loading and discharging may be significant. The morphokinetic data evaluated in developing mouse embryos has suggested that embryo hatching may be affected by embryo cooling, but further work is needed to confirm this effect. The ‘novel’ grading system proposed here combines both ETT with a systematic grading system and is based on strong evidence acquired in this work. It has been shown to be reliable and easy to use but it remains for this ‘new’ system to be tested and integrated into clinical practice.
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