Early pregnancy loss may be explained by embryo development discovery

Key molecular events regulating early embryo development have been revealed for the first time.

University of Cambridge researchers have created a detailed profile of molecular signals governing embryo implantation during the second week of embryo development. This crucial stage is the point at which many early pregnancy failures occur.

Lead author Professor Magdalena Zernicka-Goetz said: 'Implantation is a milestone in human development as it is from this stage onwards that the embryo really begins to take shape and the overall body plans are decided. It is also the stage of pregnancy at which many developmental defects can become acquired.'

Ethical and practical constraints have meant that, until now, very little had been discovered about this step because development has only been possible inside the womb. However, using a technique to culture human embryos in vitro for up to 14 days, pioneered by the same group (see BioNews 850), and the latest sequencing technology, the team were able to identify the 'molecular conversations' between embryonic cells.

'Embryo development is an extremely complex process and while our system may not be able to fully reproduce every aspect of this process, it has allowed us to reveal a remarkable self-organising capacity of human blastocysts that was previously unknown,' said co-author Dr Marta Shahbazi.

The study, published in Nature, revealed that some cells release signals instructing other groups of cells to form either the head or tail end of the developing embryo, marking the very earliest stages of body-plan coordination. These cells then respond to their instructions by transitioning out of pluripotency – the state in which cells can take on any identity – before going on to become defined parts of the developing embryo's body.

The findings, which bridge a knowledgegap in embryology, could lead to a greater understanding of why some pregnancies fail early after conception and offer insight into the causes of some developmental defects.

Co-author Dr Simon Fishel, director of CARE Fertility said 'This is about much more than just understanding the biology of implantation embryo development. Knowledge of these processes could help improve the chances of success of IVF), of which only around one in four attempts are successful.'