Human embryo research: should we re-draw the line?

In the UK, it is prohibited to culture embryos in vitro for research purposes for more than 14 days after fertilisation.


This so-called 14-day rule was implemented over 30 years ago in the Human Fertilisation and Embryology Act 1990 (HFE Act 1990), at a time when the field of embryonic research was only just emerging.

In 2016, culture techniques were developed meaning it is now technically feasible to sustain embryos in vitro beyond this two week window. Not surprisingly, there have been increasing calls for the limit to be extended ever since. Currently, researchers can only study aborted foetuses that are more than 28 days old. As such, the 14-28 day period of embryonic development remains a ‘black box’ in the field about which very little is known.

Last week, the Health Council of the Netherlands recommended that the Dutch 14-day limit should be extended to 28 days. Supporters argue that such an extension will enable the ‘black box’ to be opened, with important implications for the study of congenital disorders, infertility and miscarriage. In the UK, the Human Developmental Biology Initiative (HDBI) has recently launched a public engagement dialogue to better understand public attitudes towards embryo research. Is it finally time to re-draw the line for embryonic research?

The origins of the 14-day rule

The 14-day rule was first recommended by the Warnock Committee in their Report of 1984, not long after the birth of the world’s first IVF baby, Louise Brown, in 1978.

Grappling with utilitarian arguments in favour of embryonic research, fears over ‘unscrupulous scientists’ and moral claims that embryos should receive special protection in law, the Warnock Committee extensively debated the acceptable parameters for conducting research on embryos. In their proposal, the Committee argued that a 14-day threshold would fall before the embryo’s development of a ‘primitive streak’ – the point at which twinning is no longer possible. The Committee’s rationale was that once the primitive streak has developed, the individuality of the embryo is fixed because twins, on the other hand, would require two souls. Indeed, the Committee’s view was that the embryo could be regarded as a mere collection of cells up until the 14-day mark. The Committee also suggested that a 14-day limit would avoid any possibility of the embryo experiencing pain, since the threshold falls well prior to the formation of the central nervous system. Although the Committee acknowledged that their proposal was a compromise, by the end of the decade the 14-day rule had been duly adopted into an Act of Parliament – the HFE Act 1990 – where it remains today.

It is clear from the shaky conclusions of the Warnock Committee that the statutory 14-day limit came about as a matter of pragmatism, rather than one determined on the basis of, say, a single particularly significant stage in human development or a clear ethical framework. Yet despite this, the 14-day rule has until relatively recently inspired public confidence by providing a clear (if arbitrary) boundary for researchers and regulators alike.

The 14-day rule today

For the Warnock Committee and the original draftsmen of the HFE Act 1990, culturing embryos in vitro for longer than 14 days would have been a purely imaginary notion. Today, the debate is far from theoretical. Since 2016, techniques have been developed such that it is now feasible to culture embryos in vitro for over two weeks. In this context, the International Society for Stem Cell Research published revised guidelines in 2021 recommending meaningful public engagement to inform regulatory changes. As well as the HDBI’s recent launch of a public engagement dialogue, the Human Fertilisation and Embryology Authority (HFEA) is currently reviewing responses from a public consultation on the HFE Act 1990 held earlier this year.

Extending the 14-day window would permit research on vital developmental processes that are otherwise near impossible to study, such as gastrulation, mechanisms of implantation and the appearance of primordial germ cells. Legalising research on embryos up to 28 days after fertilisation would be extremely valuable to the field of reproductive medicine, particularly in relation to miscarriage, infertility and foetal disorders. Given the arbitrariness of the 14-day rule, it is arguably difficult to construct a compelling moral argument against extending the limit to 28 days in those jurisdictions that already permit embryonic research until 14 days.

Embryonic research is of course subject to a rigorous regulatory framework in the UK. The HFEA may grant a licence for up to three years only if it is satisfied that research is being conducted for one of a number of prescribed purposes, including increasing knowledge about serious disease, promoting advances in the treatment of infertility and developing more effective techniques of contraception. There is no compelling reason why this regulatory model could not be applied in the same manner for research up to 28 days.


The scientific case for permitting embryonic research for certain purposes beyond 14 days is very persuasive, but any attempts to redraw the line will likely be fraught with controversy. The UK’s proven regulatory capacity in embryonic research and initiatives to foster public engagement on the issue should nonetheless encourage public confidence in an extension. Most significantly, legalising research on later stage embryos will enable the advancement of our understanding of human development, as well as expanding therapeutic potential to reduce infertility, miscarriage and congenital disorders.