Scientists seek end to 14-day rule on lab-grown human embryos

Scientists called on Wednesday for a key 14-day time limit for growing human embryos in the lab to be relaxed as they outlined new ethical guidelines for the fast-changing world of stem cell research.

In its first update since 2016, the International Society for Stem Cell Research (ISSCR) said the decades-old rule had little scientific merit, although they stopped short of giving the green light for researchers to breach the time constraint, which is baked into law in some countries. For years scientists have had to infer the exact changes that human embryos go through in early development.

But new methods of culturing them in a dish -- and of creating embryo-like models using stem cells -- have enabled scientists to track this process right up to the edge of the two week limit, when the embryos must be destroyed.

It is soon after 14 days that the first signs of the central nervous system appear and the beginnings of tissues are formed. And scientists think it is during this time that problems occur that cause recurring miscarriages and congenital abnormalities, like those of the heart and spine.

There is increasing recognition of "scientific need and justification for taking it beyond 14 days into this so-called ‘black box’ period of the next two weeks, where we know very little of what’s going on in human embryos," said stem cell and developmental biologist Robin Lovell-Badge, who led the ISSCR update.

"You can also make the ethical argument that given the importance of this period to human development, we have to understand it," said Lovell-Badge, of the Francis Crick Institute in London. The 14-day rule dates back to the 1980s in Britain, when it was proposed as a way of gaining political approval for research on human embryos by ensuring that there were guardrails.