by Scientists are calling for a review of the 14-day rule for embryo research, saying extending the limit could help uncover causes of recurrent miscarriages and congenital conditions.
Until now, scientists studying the earliest stages of life were restricted to nurturing embryos up to the equivalent of 14 days of development. They can pick up the path of development several weeks later, on pregnancy scans and from material donated from termination.
But this leaves a “black box” period of between two and about four weeks of development that has never been directly studied and which scientists say could hold the key to improving fertility treatments and understanding variety of birth defects.
With reform of fertility laws on the horizon and rapid scientific progress, scientists are calling for a review of the 14-day rule.
Dr Peter Rugg-Gunn, from the Babraham Institute in Cambridge, said: “The period between two and four weeks is labeled as the black box of embryonic development. There is currently no practical way to study this so our knowledge is really limited. Studying embryos beyond the 14-day limit may provide benefits to patients. The sooner it is approved, the sooner patients in the UK could benefit from it.”
Potential benefits include finding the causes of implantation failure, where the embryo does not implant in the lining of the womb leading to miscarriage, and the origins of congenital heart defects, which affect around one in every 100 births and is estimated to be responsible for around 40% of preterm births. deaths.
“I think it’s important that people understand what the potential benefits are,” said Rugg-Gunn, who did not directly call for the extension of the limit as part of the Human Fertilization Authority’s sweeping proposals and Embryology (HFEA). to modernize the law.
The UK’s 14-day rule was first proposed in the 1984 Warnock report on the ethics and regulation of IVF technology, and has been in law since 1990. It prohibits the cultivation of embryos after 14 days of development or before the formation of the primitive streak (which establishes the axis of the body) and was intended to balance the potential medical benefits of research with the special status of the human embryo.
In 1990, however, the limit was theoretical because scientists could not sustain embryo development in the laboratory beyond a few days. Over the past five years, this has changed and there is an increasing number of laboratories around the world able to closely replicate development up to the legal limit.
“We’re now at the point where it’s technically feasible to do these experiments,” Rugg-Gunn said. “There is a high probability that if the research continued, the new knowledge would benefit health, especially to understand the causes of recurrent miscarriages.”
Just after day 14, gastrulation occurs, a major step in which the embryo changes from a simple ball of cells into three separate layers of tissue that establish a primitive body plan. “It’s one of the most important steps in all of development, but this has never been studied or visualized,” Rugg-Gunn said.
Implantation of the embryo into the lining of the womb (endometrium) occurs between days six and 12, but the process continues – and can go wrong – after day 14, and is considered a common reason why treatment does not work IVF.
Professor Kathy Niakan, a developmental biologist at the University of Cambridge, said: “There is an immunological interaction that is quite unique at that time of pregnancy. There’s this really interesting question about why, in some cases, the mother’s cells and the fetal cells can’t exist without some kind of attack or failure.”
During the third week, cells continue to differentiate and the first heart cells are formed. A high percentage of congenital heart conditions are thought to develop during this very early developmental period. Between days 21 and 28, the neural tube (the embryonic precursor of the central nervous system) forms and closes. Spina bifida is caused by the failure of the neural tube to close properly, but the precise steps have not been directly observed. From around four weeks, scientists begin to gain insights into development from pregnancy scans and embryos taken from termination.
Some argue that scientists may be exaggerating the potential clinical benefits of cultivating embryos beyond 14 days and question whether the ethical arguments underlying the legal limit have changed much.
“Borders are meaningless if they don’t prevent you from doing something,” said Professor Anna Smajdor, a philosopher at the University of Oslo. “Now [scientists] This can do things, they do not want to be limited. The danger is that it mocks the idea that these are moral cut-off points that result from honest, moral discussion with scientists.”
It is now more clear than in 1990 that an embryo does not have a functional nervous system at 28 days, but Smajdor said that the ethics do not need to be reduced to ‘does it feel pain?’. Even without a religious point of view, it is possible to think that embryos have moral value because they have the potential to become human beings. There is a symbolic component to it.”
Others suggest that the duty has changed with scientific progress. “Human embryos are a rare and precious resource,” said Sarah Norcross, chief executive of the charity Progress Educational Trust. “Is it right that scientists are legally obliged to stop studying these embryos in the laboratory after 14 days, when we could learn a lot more from them, and when we could -use this information to better understand pregnancy loss and disease?”
Many believe that, with amendments to the law on the way, it is time to at least reopen the debate. “Discussion is not the same as changing the rule,” Niakan said. “It means having an open, two-way dialogue about what might be found, what the risks might be and asking how we feel about that.”
