O brave new models

Understanding the earliest stages of human development is essential for improving reproductive health, but these stages are normally hidden from view. In this thesis, stem cell–based human embryo models were grown in the laboratory to study development from pre- to early post-implantation stages. These embryo-like structures were created using a microwell platform that allowed large numbers of models to be produced at the same time. By working with many models simultaneously, the research made it possible to study rare developmental events, such as the formation of identical twins during pre-implantation. In addition, three different embryo models were exposed to a wide range of chemical compounds to investigate how potentially harmful substances affect early development across different stages and cell types. This approach may help improve the safety testing of medicines and environmental chemicals. Finally, the thesis explored the use of soft gel-like materials, called hydrogels, to mimic the natural environment of the uterus. Together, these advances show how embryo models can support research aimed at improving reproductive health and pregnancy outcomes.