A team of researchers led by Professor Magdalena Zernicka-Goetz used stem cells to develop the embryo model, rather than eggs or sperm. Stem cells are master cells which can develop into almost any other cell type in the body.

Model embryos, such as those grown by the researchers, could help further understandings of why some embryos go on to develop into a healthy pregnancy, while others do not. The results could also be used to guide repair and development of synthetic human organs to be used in transplants.

To create the embryos, researchers mimicked natural processes to guide three types of stem cells found in early development of mammals until they started interacting. The researchers could get the stem cells to 'talk' to each other by manipulating genes and establishing the right environment for the cells.

From there, the stem cells organised themselves into structures that developed beating hearts and the foundations of the brain. They also grew the yolk sac where embryos get nutrients from during their first few weeks of life.

In a research first, these embryos reached a point where the entire brain, including the front portion, began to develop. No other stem-cell derived model has ever reached this stage.

Professor Zernicka-Goetz's group in Cambridge has been studying these earliest stages of pregnancy for a decade. They want to understand why some pregnancies fail and some succeed.