Infertility is a critical component of reproductive health and remains a highly prevalent global condition. In many cases, couples with infertility may choose assisted reproductive technology (ART) to increase their chances of conception. However, an increasing application of ART treatment worldwide has also generated both scientific and public interest in its efficacy and safety. Since successful development of embryos in vitro is one of the key steps in ART and has a crucial influence on pregnancy outcome, an improved understanding of these processes will help us figure out the underlying mechanisms in ART failure due to poor embryonic development, especially for couples without normal embryos for transfer in several cycles.
In this thesis, I discuss maternal and paternal contribution to the development of human preimplantation embryos. Firstly, I give a brief introduction to the present clinical status of infertility and great concerns in the field of ART. Secondly, I systematically introduce the developmental process of human preimplantation embryos, including maturation of gametes, the process of fertilization, the dynamic reprogramming of epigenome upon fertilization, the transcriptional activation of embryonic genome, and the lineage differentiation of embryos at the blastocyst stage. Lastly, I summarize the clinical situation and scientific findings of couples suffering from recurrent ART failure due to poor embryonic development.
Next, I present our findings on the maternal and paternal contribution to human embryogenesis based on the dynamics of parental-of-origin sex chromosomes, as well as the effects of parental genetic background on embryonic development. The distinct activation and silencing of sex chromosomes result in an imbalanced dosage of gene expression, and thus, have potential effects on the sex-specific behaviour of early embryos. The analysis of couples with recurrent poor embryonic development indicate that they are highly heterogeneous both phenotypically and genetically. These results will further knowledge within the ART field and possibly improve the treatment of infertility. Our findings also enable potential application of whole genome sequencing to clinical diagnosis and it could contribute to improve genetic counselling of couples with a history of ART failure. Hence, all the results will possibly expand the capabilities of ART and enhance reproductive health.