by Scientists are calling for a review of the 14-day rule in embryo research, saying extending the limit could help uncover the causes of recurrent miscarriages and congenital diseases.
Until now, scientists studying the early stages of life have been limited to growing embryos up to the equivalent of 14 days of development. They can then get back on track several weeks later, based on pregnancy scans and donated material after interruptions.
But this leaves a “black box” period of two to about four weeks of development that has never been directly studied and which scientists say could be the key to improving fertility treatments and understanding a variety of birth defects. .
With a review of fertility laws on the horizon and rapid scientific advances underway, scientists are calling for a review of the 14-day rule.
Dr Peter Rugg-Gunn, from the Babraham Institute in Cambridge, said: “The two to four week period has been called 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 could provide benefits to patients. The sooner this is allowed, the sooner patients in the UK can benefit.”
Potential benefits include finding the causes of implantation failure, when the embryo fails to embed in the lining of the uterus causing miscarriage, and the origins of congenital heart defects, which affect approximately one in 100 births and are estimated to They are responsible for around 40% of prenatal pregnancies. deceased.
“My view is that it is important for people to understand what the benefits could be,” added Rugg-Gunn, who stopped short of directly calling for an extension of the limit as part of radical proposals from the Human Fertilization and Embryology Authority (HFEA). modernize the law.
The UK’s 14-day rule was first proposed in the 1984 Warnock report into the ethics and regulation of IVF technology, and has been law since 1990. It prohibits the cultivation of embryos beyond 14 days development or before the formation of the primitive streak (which establishes the axis of the body) and aimed to balance the possible medical benefits of research with the special status of the human embryo.
In 1990, however, the limit was theoretical because scientists could not sustain embryonic development in the laboratory beyond a few days. In the last five years, this has changed and a growing number of laboratories around the world are able to faithfully replicate the development up to the legal limit.
“We’re at a point where technically these experiments are probably possible,” Rugg-Gunn said. “There is a very high probability that, if research could continue, the new knowledge would have health benefits, particularly in understanding the causes of recurrent miscarriages.”
Shortly after day 14, gastrulation occurs, a momentous step in which the embryo transforms from a simple ball of cells into three distinct layers of tissue that establish a primitive body plan. “It’s one of the most important steps in the entire development, but it’s never been studied or visualized before,” Rugg-Gunn said.
Implantation of the embryo into the lining of the uterus (endometrium) occurs between day six and day 12, but the process continues (and can go wrong) beyond day 14, and is thought to be a common reason why IVF treatment does not work.
Professor Kathy Niakan, a developmental biologist at the University of Cambridge, said: “There is an immune interaction that is really unique at that point in pregnancy. “There’s a really interesting question as to why, in some cases, maternal cells and fetal cells can’t coexist without some kind of attack or failure.”
During the third week, cells continue to differentiate and the first heart cells form. It is believed that a high proportion of congenital heart diseases arise during this very early period of development. Between days 21 and 28, the neural tube (the embryonic precursor of the central nervous system) forms and closes. Spina bifida is caused by a failure of the neural tube to close properly, but the precise steps have not been directly observed. Starting at about four weeks, scientists begin to obtain information about development from pregnancy scans and embryos donated after abortions.
Some argue that scientists may be exaggerating the potential clinical benefits of growing embryos beyond 14 days and question whether the ethical arguments supporting the legal limit have really changed.
“Limits are meaningless if they don’t actually stop you from doing something,” said Professor Anna Smajdor, a philosopher at the University of Oslo. “Now [scientists] They can do these things, they don’t want to be limited. “The risk is that it makes a mockery of the idea that these are moral cut-off points that are the product of honest moral deliberation with scientists.”
It is clearer now than in 1990 that an embryo does not have a functional nervous system at 28 days, but Smajdor said the ethics at play “are not necessarily reducible to ‘do you feel pain?'” Even without a religious perspective, it is possible to think that embryos have moral value because they have the potential to become human beings. “It has a symbolic component.”
Others suggest that with scientific advances, responsibility has changed. “Human embryos… are a rare and valuable resource,” said Sarah Norcross, chief executive of the charity Progress Educational Trust. “Is it right that scientists are legally required to stop studying these embryos in the lab after 14 days, when we could learn so much more from them and when we could use this knowledge to better understand pregnancy loss and disease?”
Many believe that with reforms to the law on the way, it is at least time to reopen the debate. “Having the discussion doesn’t mean the rule is going to change,” Niakan said. “It means having an open, two-way dialogue about what could be gained, what the potential risks are, and asking how we feel about it.”
