Scientists have created synthetic human embryos using stem cells, in a groundbreaking advance that sidesteps the need for eggs or sperm. These model embryos resemble those in the earliest stages of human development. They could provide a window on the genetic disorders and biological causes of recurrent miscarriage. However, the work also raises serious ethical and legal issues as the lab-grown entities fall outside current legislation in the UK and most other countries. The structure’s heart does not beat and it has no brain, but it does include cells that would go on to form the placenta, yolk sac and the embryo itself. Prof Magdalena Żernicka-Goetz, of the University of Cambridge and the California Institute of Technology, described the work as creating human embryo-like models by the reprogramming of embryonic stem cells. There is no immediate prospect of the synthetic embryos being used clinically. It would be illegal to implant them into a patient’s womb.