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By Roger Highfield on

How long should we grow human embryos in the lab?

Roger Highfield discusses the ethical dimensions of reproductive science to mark our new exhibition, IVF: 6 Million Babies Later.

The ‘14-day rule’ is a widely observed ethical line past which human embryos are not allowed to be grown outside the body, and has been enshrined in law in 12 countries, including the United Kingdom. However, recent advances in our ability to grow human embryos in the laboratory have led to calls for the 14-day rule to be relaxed.

It was Baroness Mary Warnock, an English philosopher of morality and education, who in 1984 led a committee which explored the borderlands that lie between acceptable and unacceptable research on the human embryo.

Remarkably, the UK still abides by their recommendations, which were enshrined in the UK in the Human Fertilisation and Embryology Act in 1990, making Warnock arguably the most influential proponent of applied bioethics in recent decades.

In her original report, Warnock came up with a practical way for society to deal with the ethical and moral fallout of the most momentous event in human embryology, the birth of the first IVF baby, Louise Brown, by reconciling the irreconcilable: the views of religious fundamentalists who treated the early embryo as a person, and scientific pragmatists who regarded it as a collection of cells. Then she had to build a bridge of consensus for how to regulate this work between the public, media, parliamentarians and the scientists.

Once the euphoria surrounding the birth of Louise Brown in 1978 had abated, concerns about growing human embryos in the laboratory for experiments would steadily grow. There was a perception that scientists could not be certain of the outcome of implanting artificially-conceived embryos, indeed many were appalled by the thought that scientists could discard living embryos that were deemed imperfect. Some, as Warnock put it, thought that this was tantamount to ‘throwing a baby away.’ Consternation followed the admission by Edwards in a February 1982 television documentary that he had experimented on embryos he had no intention of implanting into patients: ‘they can teach us things about early human life’.

In June of 1982 Norman Fowler, the Government’s Secretary of State for Health and Social Services, wrote to Warnock, then a University of Oxford philosopher and educationalist, to invite her to advise ministers on whether IVF should be banned and, if it did go ahead, how it should be regulated. Warnock had huge respect for the public who she believed were ‘entitled to know, and even to control’ professional practices, an appetite for public engagement that feels very contemporary.

Warnock herself was ‘completely ignorant’ about embryology and the earliest stages of human development and, despite the broad representation on her select committee, she needed help. One member alone would prove crucial to the outcome of her inquiry: the Cambridge University developmental biologist, Anne McLaren.

In recognition of how the early embryo is not the same as a person, or a child, 14 days was adopted as the limit for embryo research. In paragraph 45, the Warnock report recommended that ‘it be a criminal offence to handle or to use as a research subject any live human embryo derived from in vitro fertilisation beyond that limit (i.e. fourteen days after fertilisation)’.

The 14-day limit was chosen for good reason. First, Mary Warnock wanted an unequivocal limit that rested on a defined period rather than a stage of development, which could at best be open to interpretation. Moreover, 14 days was around that time a human embryo elongates and develops a line called the primitive streak, which marks a channel where the spinal cord will eventually grow. Some have described this as the first developmental stage at which the embryo can develop into a more complex organism which can plausibly be nothing other than a human being.

The reception to her report was, she admits, mixed. Of all her opponents perhaps the most implacable was the chief rabbi, Immanuel Jacobowitz. He mounted attack after attack – one  Times article carried the headline ‘Warnock destroys morality’. This headline, she recalled with a wry smile, delighted her husband Geoffrey, a fellow philosopher and then Vice-Chancellor of the University of Oxford.

When the legislation eventually came before them, parliamentarians were offered a choice between prohibiting all embryo research and permitting it in defined circumstances.  By then the public debate had moved on, focusing now on the possibilities of adapting the now established method of IVF to screen embryos for genetic disease. Aware of the possibilities, parliamentarians chose the latter course to allow IVF and experimentation but legislated that embryos could not be kept or used ‘after the appearance of the primitive streak’.  The 14-day limit became law.

In recent years, Warnock believes that her report has held up ‘quite well, particularly the 14-day rule’. She told me that if ever she feels despondent, she reassures herself by thinking about her report: ‘Well, at least I did that’.

But even the Warnock report envisaged that a day would come when the 14-day limit would be challenged with ‘the maintenance of developing embryos in an artificial environment (ectogenesis) for progressively longer periods’. Only recently has it become possible to grow embryos for longer than 14 days, in the light of recent work in the University of Cambridge by Magdalena Zernicka-Goetz and in America and this could pave the way for research to improve IVF efficacy by identifying markers of successful development, help understand the causes of early embryo loss in pregnancy end the misery of miscarriage, and further understand the effects of drugs, alcohol and toxic compounds in embryos.

Baroness Warnock agrees that there is a great deal that could be learned by extending this limit but argues that the public need more time to understand the basics of what was being proposed and what scientists want to do with embryos grown for longer in the laboratory. If this advance in growing human embryos immediately prompted a loosening of legislation to, say, a 21-day limit, then it would stir ever-present fears about sliding down the ‘slippery slope’.

In the longer term, there are other points at which a line might be drawn to curb embryo research, and these were also explored by the Warnock Committee. Perhaps in the beginnings of a central nervous system (at around 22–23 days) or much later, when functional activity in the brain can show if pain could be felt (today we know that connections to the cortex are not intact before 24 weeks of gestation and, as most neuroscientists believe that the cortex is necessary for pain perception, the foetus cannot experience pain in any sense prior to this point in gestation).

Decades later, the thinking in the Warnock report remains as relevant as ever.

Baroness Warnock is a Patron of the Progress Educational Trust and winner of the Dan David Prize in 2018.


IVF: 6 Million Babies Later opens 5 July to mark the 40th birthday of in vitro fertilisation. Celebrate at a special Lates event in conversation with Louise Brown and Roger Gosden. Book your free ticket here