A debate is needed over embryo research limits

Since serious experiments in human embryology began in the late 1970s, researchers and regulators around the world have stuck to a “14-day rule”: no embryo can be kept alive for more than two weeks after its creation in the lab. Now the science has moved on far enough to prompt discussions on doubling that limit. Pressure for a change is building among scientists, with support from some bioethicists, who say that a new 28-day rule could deliver considerable benefits for the treatment of infertility and developmental disorders, as well as for biomedical research more broadly. But they are cautious about campaigning publicly to expand the scope of human embryo research, a subject that remains almost as controversial as it was when the IVF era dawned 40 years ago.

A backlash could end up further restricting their work.Although it may be too soon for a full-blooded campaign to allow scientists to grow human embryos to 28 days, the time has come to initiate a public debate on the issue. Those who favour extending the permitted period for embryo research could then explain the expected benefits, while opponents marshal reasons — moral or scientific — for maintaining the status quo. Bodies such as the US National Academy of Medicine, the UK Academy of Medical Sciences and the Nuffield Council on Bioethics, which have led the debate over the related issue of human gene editing, should take the lead. If an open and wide-ranging discussion shows public support for change, legislators and regulators could take appropriate action, leading to a new international standard for embryo research.The 14-day rule started life soon after the birth in 1978 of Louise Brown, the first “test-tube baby”, showed that healthy human embryos could be created in the lab. Though the original aim of IVF work was to implant the new embryo into a womb to grow into a baby, it was immediately clear that IVF embryos could also be used for research to improve assisted reproductive technology — and that a limit must be imposed, above all to reassure the public that Frankenstein-type research was out of bounds.Two weeks was chosen partly because there was then no scientific prospect of sustaining an embryo for that long outside the body, and partly because 14 days marks the point at which an embryo cannot split to become twins and therefore may be regarded as a human individual.Research within 14 days has been enormously productive, yielding much clinically useful knowledge about early embryonic development, but experiments are now bumping up against the limit.

With today’s technology it would be possible to study embryos for longer — and 28 days is emerging as a possible new limit. At four weeks the embryo’s organs are forming and it already has a heartbeat, but it does not have functioning neural connections or sensory systems that could give rise to sentience, pain or suffering.Studies of slightly older embryos could shed light into what has been called a “black box” of development between two and four weeks, before natural embryos from miscarriages are available to study. Stem cells and gene editing, combined with extended embryo research, offer exciting prospects for improving assisted human reproduction. But advocates of a new 28-day limit will have to make a strong case, in the face of inevitable arguments by their opponents that it would be a step down a slippery slope to lab-grown babies. Opinion surveys show support for embryo research, if well regulated, but scientists cannot take public approval for granted.