Scientists yesterday reported they had grown human embryos in the lab for nearly two weeks, an unprecedented feat that promises advances in assisted reproduction, stem-cell therapies and the basic understanding of how human beings form.

Besides opening a window onto the first steps in the creation of an individual, the findings in parallel studies may help explain early miscarriages and why in vitro fertilisation has such a high failure rate. The research also showed for the first time that newly-forming human embryos can mature beyond a few days outside a mother’s womb, something that was previously thought to be impossible.


But the widely hailed results also set science on a collision course with national laws and ethical guidelines, experts cautioned.

Up to now, a so-called “14-day rule” – which says human embryos cannot be cultured in the lab for more than two weeks – has never been challenged because no one had succeeded in keeping them alive that long. In this case, the scientists destroyed the embryos to avoid breaching that limit.

The findings were published in Nature and Nature Cell Biology.

Next to nothing is known about how the small, hollow bundle of cells called a blastocyst – emerging from a fertilised egg – attach to the uterus, allowing an embryo to begin to take shape.

“This portion of human development” – called implantation – “was a complete black box”, said Ali Brivanlou, a professor at The Rockefeller University in New York, main architect of the study.

Building on previous work with mice, Brivanlou and colleagues concocted a chemical soup and scaffolding to duplicate this process “in vitro”, or in a petri dish.

“We were able to create a system that properly recapitulates what happens during human implantation,” said Rockefeller scientist and lead author Alessia Deglincerti.

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