Policymakers urged to extend the 14-day limit on embryo research

The 14-day limit on culturing human embryos in the lab should be extended, according to an international group of researchers.

Scientists, clinicians and ethicists from the US, UK, Netherlands and China have called on policymakers, including the International Society for Stem Cell Research (ISSCR), to provide a cautious framework for culturing human embryos beyond 14 days. They argue that permitting research after 14 days could allow greater scientific exploration of developmental disorders and fertility.

The 14-day limit 'never stood as a philosophical position that the embryo gained an inviolable degree of moral status at that developmental point,' according to the authors, lead by Insoo Hyun, professor of bioethics and philosophy at Case Western Reserve University School of Medicine in Cleveland, Ohio. Rather, the timeframe's conception was arbitrary or used to conveniently integrate with existing local policy.

The current ISSCR policy restricts the study of development beyond the formation of a structure termed the primitive streak, however, the organisation is soon to publish updated guidelines. 

The article, published in Science, proposes six founding principles for research that continues beyond the two-week limit, including the requirement for strong scientific justification with aims that cannot be met through similar models. Extending culture periods must also be gradual, with frequent regulatory evaluations, to assess the viability of embryos and whether the data justifies their experimental use. Considering current knowledge of embryogenesis, the researchers believe 'increments of two or three days linked to defined developmental milestones seem appropriate.'

Furthermore, they suggested research proposals must be independently peer-reviewed by qualified ethics committees, which may be provided by the ISSCR, and any advances be preceded and informed by broad public discourse. Other principles highlighted the importance of consent from donors or those with authority over IVF embryos and the 'process of obtaining consent for embryo research must be kept separate from any clinical decisions for fertility treatments.'

The period between 14–28-days after fertilisation is known as the 'black box' of human development because so little is known about it. 

The authors discussed the use of alternative models, explaining that 'monkey embryos implant on the surface of the endometrium, whereas human embryos (as well as those of apes) implant within the endometrium and this process might be relevant for disorders such as intrauterine growth restriction, which keeps babies from reaching a healthy birth weight.' For stem cell models, parallel human embryo experiments would be essential, at least initially, for validating their development. 

The authors, therefore, concluded that extending human embryo experiments beyond 14 days provides an irreplaceable opportunity to study human development and address fertility-related disorders. After careful consideration, they stated that 'an incremental approach seems to be our only path forward, both from a scientific and a policy standpoint.'

The 14-day rule is incorporated in law in many jurisdictions, including the UK, so a change in ISSCR recommendations would not immediately affect restrictions on UK-based researchers. There have also been other calls for this law to be reviewed (see BioNews 1083).