The first weeks after a sperm fertilises an egg is a period of dramatic change - from a collection of indistinct cells to something that eventually becomes recognisable on a baby scan.

Instead of a sperm and egg, the starting material was naive stem cells - reprogrammed to gain the potential to become any type of tissue in the body.

Despite the late-night video call, I can hear the passion as Prof Hanna gives me a 3D tour of the “exquisitely fine architecture” of the embryo model.

The hope is embryo models can help scientists explain how different types of cell emerge, witness the earliest steps in building the body’s organs or understand inherited or genetic diseases.

There is even talk of improving in vitro fertilisation (IVF) success rates by helping to understand why some embryos fail or using the models to test whether medicines are safe during pregnancy.

Prof Alfonso Martinez Arias, from the department of experimental and health sciences at Pompeu Fabra University, said it was “a most important piece of research”.

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