Why we should not extend the 14-day rule

By Bruce P. Blackshaw

In 1978, the first baby conceived by IVF was born in the UK, and public concern about how rapidly science was advancing resulted in a government inquiry being set up. It produced the Warnock Report, which recommended (amongst other things) that human embryos could be cultured in vitro for no longer than 14 days. The report was very successful—it set some firm limits to scientific research that helped to alleviate public concern, and researchers were satisfied because the 14-day limit was far beyond what was actually possible. The 14-day rule was widely adopted around the world, and for almost 40 years has had few critics.

However, this is changing. In 2016 it became possible to culture human embryos for longer than 14 days, and unsurprisingly, some researchers are now pushing to have the limit extended, so as not to hamper future research.

In our paper ‘Why we should not extend the 14-day rule’ we explain why we don’t think this is a good idea, by looking at the reasoning behind the Warnock Committee’s recommendation. They had a tricky problem to solve—reconciling a wide range of incompatible views about the status of human embryos. Some committee members thought that embryos should never be used in research, while the majority thought it was acceptable if done under fairly strict conditions. The inevitable result was a clever fudge—the 14-day rule. It was known that up to 15 days or so, embryos could split, resulting in twins. The report argued that this meant the embryo was not a unique individual until twinning was no longer possible. As we explain in our paper, this reasoning is dubious, and it seems the majority of the committee saw it as a convenient way to justify a 14 day limit. Nonetheless, the 14-day rule has become a widely accepted standard.

Now that arguments are being made to extend the rule to 28 days, we need to know how to evaluate them. In our view, the logical approach is to apply the Warnock committee’s original reasoning. Although we believe it to be flawed, in a pluralistic society it is not clear how it can be improved upon. Opinions on the status of human embryos are as diverse as ever, and public concern about the boundaries of scientific research is still an important issue. So, in our response to Sophia McCully’s argument for extending the limit, we examine how her approach compares with that of the Warnock committee.

In our estimation, McCully doesn’t really engage with the Warnock committee’s reasoning, preferring to list the potential benefits of an extension to the rule. Unfortunately, this does little to alleviate public mistrust of science—it’s easy to think of benefits for almost any research, no matter how dubious. In our view, there is little need for an extension right now, and an extensive public debate is required prior to any decision being made.


Paper title: Why we should not extend the 14-day rule

Author(s):  Bruce P. Blackshaw and Daniel Rodger

Affiliations: University of Birmingham, United Kingdom, and London South Bank University, United Kingdom.

Competing interests: None


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