Bioethicists criticized Thursday the relaxation of a 14-day limit on human embryo experimentation.

In a June 3 statement, the Anscombe Bioethics Centre in Oxford, England, lamented the decision by the International Society for Stem Cell Research (ISSCR) to lift the limit on lab-grown embryo experimentation.

“Once the 14-day rule falls away, the only real limit, it seems, to experimentation would be the scientific limit as to how long embryonic or fetal human beings can be sustained outside the womb — or, indeed, in an artificial womb (ectogenesis),” said the center’s director, David Albert Jones.

The ISSCR, an independent nonprofit organization based in Skokie, Illinois, announced on May 26 that it was relaxing the decades-old rule due to rapid advances in the field.

Jones said that the ISSCR “Guidelines for Stem Cell Research and Clinical Translation” place no time limit on culturing human embryos.

“These new proposals constitute a rule on embryo experimentation that is, in effect, a shifting goalpost,” he wrote. 

“Considering that abortion is legal up to 24 weeks in Britain, or up to birth for babies with disabilities, one must wonder what principle would protect unborn infants from experimentation up to, or beyond, these same limits.”

The ISSCR’s 2016 guidelines prohibited experiments on human embryos “beyond 14 days or formation of the primitive streak, whichever occurs first.”

The new guidelines call on “national academies of science, academic societies, funders, and regulators to lead public conversations touching on the scientific significance as well as the societal and ethical issues raised by allowing” experiments beyond 14 days.

“Should broad public support be achieved within a jurisdiction, and if local policies and regulations permit, a specialized scientific and ethical oversight process could weigh whether the scientific objectives necessitate and justify the time in culture beyond 14 days, ensuring that only a minimal number of embryos are used to achieve the research objectives,” the guidelines state. 

Jones said that when the U.K. legalized experiments on human embryos in 1990, it promised that they would be subject to strict conditions. But he noted that safeguards had gradually fallen away. 

“Nonetheless, to this day, the 14-day rule on experimentation has survived, though not out of principle, but simply because until recently scientists had been unable to culture a human embryo for more than 13 days,” he said. 

“In effect, the rule has been like a speed limit that no car could physically achieve. It was a vacuous prohibition, forbidding the impossible and allowing experimentation on human embryos at every stage that this was physically possible.”

He continued: “Now that scientists have finally reached this limit — which means the 14-day rule has actually become a real prohibition, and might prevent some human embryos from being experimented on — advocates of embryo experimentation are calling for this limit to be extended.” 

“Four years ago, in the United Kingdom, some had started to call for the 14-day rule to be extended to 28 days. Yet this would clearly be mere lip service to the need for ethical restraints. Could anyone believe that the 28-day rule would stay in place, if the 14-day rule was to be amended to accommodate new technological developments?” 

Jones concluded: “The further the limits of research are pushed, the more scientists will be confronted with research subjects that look more recognizably human.” 

“To experiment on human embryos that are up to 14 days old — extremely vulnerable human lives — is already a grave injustice and a form of exploitation.” 

“Extending the 14-day rule would make more embryos vulnerable to exploitation and strip away one of the few remaining limits to injustices committed against embryonic human beings.”