The time has come to extend the 14-day limit.

For the past 40 years, the 14-day rule has governed and, by defining a clear boundary, enabled embryo research and the clinical benefits derived from this. It has been both a piece of legislation and a rule of good practice globally. However, methods now allow embryos to be cultured for more than 14 days, something difficult to imagine when the rule was established, and knowledge gained in the intervening years provides robust scientific rationale for why it is now essential to conduct research on later stage human embryos. In this paper, I argue that the current limit for embryo research in vitro should be extended to 28 days to permit research that will illuminate our beginnings as well as provide new therapeutic possibilities to reduce miscarriage and developmental abnormalities. It will also permit validation of potentially useful alternatives. Through consideration of current ethical arguments, I also conclude that there are no coherent or persuasive reasons to deny researchers, and through them humanity, the knowledge and the innovation that this will generate. © Author(s) (or their employer(s)) 2021. No commercial re-use. See rights and permissions. Published by BMJ.