Scientists have grown a complete model of an early human embryo without using sperm, eggs or a womb.
Researchers at the Weizmann Institute of Science in Israel made the models using stem cells in the lab and grew them outside the womb, paving the way for advances in fertility and transplants.
The research, published in the journal Nature, found the synthetic embryo models had all the elements a 14-day human embryo would be expected to have, including the placenta, yolk sac and chorionic sac.
Professor Jacob Hanna, who led the research team, said little was known about an early embryo as it was so difficult to study, for both ethical and technical reasons.
"The drama is in the first month. The remaining eight months of pregnancy are mainly lots of growth," he said.
"But that first month is still largely a black box. Our stem cell-derived human embryo model offers an ethical and accessible way of peering into this box.
"It closely mimics the development of a real human embryo, particularly the emergence of its exquisitely fine architecture."
The researchers built on previous experience when creating the synthetic stem cell-based models of mouse embryos.
They did not use fertilised eggs or a womb, instead they started out with pluripotent stem cells, taken from adult skin cells.
"An embryo is self-driven by definition; we don't need to tell it what to do – we must only unleash its internally encoded potential," Hanna said.
"It's critical to mix in the right kinds of cells at the beginning, which can only be derived from naïve stem cells that have no developmental restrictions. Once you do that, the embryo-like model itself says, 'Go!'"
The study has already produced a finding that may open a new direction of research into early pregnancy failure, according to researchers.
"Many failures of pregnancy occur in the first few weeks, often before the woman even knows she's pregnant," Professor Jacob Hanna, who led the research team, said in a statement.
"Our models can be used to reveal the biochemical and mechanical signals that ensure proper development at this early stage, and the ways in which that development can go wrong."