Should we extend the 14-day period for cultivating human embryos?

In the Human Fertilisation and Embryology Act 1990, Parliament prohibited the in vitro culture of human embryos beyond 14 days from conception. This 14-day limit first appeared in the 1984 report of the Committee on Human Fertilisation and Embryology (the 'Warnock Report'), which the Thatcher government established following the world's first IVF birth in 1978.

Legally, the prohibition is about as fascinating as a brick wall. (Client: 'Can I culture my embryos beyond day 14?' Lawyer: 'No.') Moreover, it was until today a distinctly theoretical question too, because human embryos survive in vitro for at most five to six days. But that has changed now.

Professor Magdalena Zernicka-Goetz's work is remarkable for the discoveries made in the study of human embryos over longer periods (1,2). She reminds us that with so much to discover between the 7th and 13th days of development, there should be no urgent need to push for an extension beyond 14 days.

For the first time, it will be possible to follow development up to and beyond the time at which implantation would normally take place, allowing researchers to understand the processes of miscarriage and infertility far better and to devise new approaches to treating them. It also opens up the prospect of creating improved progenitor stem cell lines (who needs to go beyond 14 days anyway?).

Nevertheless, the advance does imply the possibility that human embryos might survive in vitro for 14 days or longer, that more valuable medical insights might be gained as a result, and that embryologists might one day correct genetic defects in more differentiated tissues (for example, using CRISPR-Cas9) so as to avoid problems later on in life without rendering those changes heritable.

In short, it's arguable that potentially significant advances in medicine are prevented by the 14-day limit. You'd therefore expect the limit to have a sound basis.

It doesn't.

In recommending the 14-day limit, the Warnock Committee focused on a particular moment in vertebrate development known as gastrulation, which begins 14 days after conception. As cells pour inwards across the embryonic disc and dive together to create a middle layer, fluid grooves called 'primitive streaks' appear on its surface. One primitive streak means one potential body, one potential person and one potential you.

As the biologist Lewis Wolpert famously remarked of this embryonic inpouring, 'it is not birth, marriage or death, but gastrulation, which is truly the most important time in your life'. In effect, the Warnock Committee took Wolpert's quip seriously, Parliament followed its recommendation and that is why we have the 14-day limit.

The 'latest stage at which identical twins can occur' (3) seems an odd rationale for a rule of such impact, especially given that no individual could ever occur in a research context anyway. This arbitrariness may explain why so many people in my own experience seem to think that the 14-day limit is justified on an entirely different basis: the appearance of a nervous system. It's easy to get the 'aha!' moment - 'primitive streak? That's the nervous system being laid down, right?'

Wrong. As any embryology textbook makes clear, this is a long way in the future. Indeed, as the Warnock Report itself observed:

'The primitive streak is the first of several identifiable features which develop in and from the embryonic disc during the succeeding days, a period of very rapid change in the embryonic configuration. By the seventeenth day the neural groove appears and by the twenty-second to twenty-third day this has developed to become the neural folds, which in turn start to fuse and form the recognisable antecedent of the spinal cord.' (4)

It's better seen visually, and better understood with reference to the transcription factors, regulatory networks and genes involved. But at its simplest, there is no one there. Even after 24 days, nothing exists to know, feel or suffer but the human dignity accorded to it by our own minds.

That dignity has grown in the 32 years since the Warnock report, but in different directions. While the Committee deliberated in London, the Vatican (not coincidentally) reversed a centuries-old doctrine of deferred ensoulment by declaring human life to be sacred from the moment of conception, a position it has sought to shore up ever since with claims to the alleged dignity and personhood of fertilised eggs (5). Meanwhile, as the influence and standing of the Church has waned, secular notions of dignity have waxed, inspired by the potential of stem cell and genetic research to reduce the human suffering that Catholics judge to be good for the soul.

In short, things have moved on a great deal since the Warnock Report. As a lawyer, my job remains unchallenged by prohibitions. But as a lawyer practising in the field of biomedicine and emerging technologies, the ban feels strangely hollow now. The advances implied by Zernicka-Goetz and others, the opportunities to undertake valuable medical research and our changed sense of values all demand that we reappraise the 14-day limit.

No, it's not urgent. Today we should celebrate fully the opening of a new chapter in embryology for which no extension of the 14-day limit is required at all. It is a truly wonderful moment, filled with possibility, just as it is.

Nevertheless, we must recognise that technologies which might enable us to study the origins of conditions such as spina bifida, the sequestration of germ cells and the cause of twinning, beside other unknowns, is emerging fast. The law needs to be ready to meet these challenges as they mature.