A joint team of scientists from the US and the UK have created synthetic human embryos using stem cells, in a groundbreaking advance that sidesteps the need for eggs or sperm.

These lab-grown structures resemble the earliest stages of human development and offer a valuable opportunity to study genetic disorders and the underlying causes of recurrent miscarriage.

"Our human model is the first three-lineage human embryo model that specifies amnion and germ cells, precursor cells of egg and sperm," Professor Magdalena Żernicka-Goetz, of the University of Cambridge at the International Society for Stem Cell Research's annual meeting in Boston.

Zernicka-Goetz discussed their latest work, which involved cultivating the synthetic embryos to a stage just beyond the equivalent of 14 days of development in natural embryos.

Stem cells have the capacity to become any cell-type in the body and if coaxed in just the right way can be persuaded to form embryos. This is the first time that has been achieved using human material. Although, they are not truly "synthetic", as the starting material was cells cultured from a traditional embryo in the laboratory. 

Prof Zernicka-Goetz has already developed synthetic mouse embryos with evidence of a developing brain and beating heart.

The rapid progress in this field has outpaced existing legislation, prompting scientists in the UK and other countries to establish voluntary guidelines for research on synthetic embryos. There are concerns that if these models closely resemble natural embryos, they should be subject to similar regulations. The unanswered question remains whether these structures can develop into living creatures. 

Scientists are uncertain whether the barriers to advanced development are technical or have deeper biological roots, underscoring the need for more comprehensive legislation in this area.