An international guide for stem cell research has released a new guide that creates conditions for removing a long-standing barrier and allowing human embryos to grow for more than the current acceptable 14 days, but in certain conditions, the Associated Press reported.

This moral standard has existed for decades, and in some countries it has even been included in legislation. Some scientists insist that this be changed to study the development of the embryo, but their opponents say that such experiments pass more easily than ethical and that it is not clear whether change will advance research.

Robin, a level-badge and association chairman at the Creek Institute in London, said the 14-day limit was set unilaterally to block research for 14 to 28 days in the next phase of embryonic development.

The guide has not been updated since 2016. It is published by the International Stem Cell Research Association, whose standards are generally accepted by states, medical journals and professionals. However, this does not make clear what the new frontier is.

Before changing the rules, there should be a broad public discussion and a specific regulatory process should be defined.