Human embryos have been kept alive in a petri dish for an unprecedented 13 days, allowing scientists to finally see what happens in the mysterious days after implantation in the womb.

Cambridge University have created a special thick soup of nutrients which mimics the conditions in the womb, allowing the embryo to attach, and begin dividing into groups of cells which will eventually form the foetus, placenta and yolk sac.

Previously an embryo had to implant in the womb by day seven to survive, but it is impossible to see what is happening inside the mother at this stage, so scientists were in the dark about the cellular and molecular changes taking place.