Scientists are calling for a review of the 14-day rule for embryo research, saying extending this limit could help uncover the causes of recurrent miscarriages and congenital disorders.
Until now, scientists studying the earliest stages of life have been limited to growing embryos with the equivalent of 14 days of development. Then, a few weeks later, they can catch up on their developmental path thanks to pregnancy scans and materials donated without terminating the pregnancy.
But this leaves a “black box” period, meaning a two- to four-week developmental period, that has never been directly studied and which scientists say could hold the key to improving fertility treatments and understanding various birth defects.
With an overhaul of fertility laws on the horizon and rapid scientific advances continuing, scientists are calling for a review of the 14-day rule.
Dr Peter Rugg-Gunn, of the Babraham Institute in Cambridge, said: “The period from two weeks to four weeks has been labeled as the black box of embryo development. There’s currently no practical way of studying this, so our knowledge is really limited. “The period from two weeks to four weeks has been labeled as the black box of embryo development. There’s currently no practical way of studying this, so our knowledge is really limited. “Studying it could benefit patients. The sooner this is allowed, the sooner patients can benefit in the UK.”
Potential benefits include finding the causes of implantation failure, where the embryo implants in the uterine wall and causing miscarriage, and the origins of congenital heart defects, which affect about one in 100 births and are estimated to be responsible for about 40% of prenatal cases. deaths.
“In my view, it’s important for people to understand what the benefits could be,” added Rugg-Gunn, who refrained from directly calling for an extension of the limit as part of the Human Fertilization and Embryology Authority’s (HFEA) comprehensive proposals. Modernizing 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 law since 1990. It prohibits growing embryos after 14 days of development or before the formation of the primitive streak (which forms the body’s axis) and was intended to balance the potential medical benefits of the research with the special status of the human embryo.
But in 1990, this limit was theoretical because scientists could not continue embryo development in the laboratory for more than a few days. This has changed in the last five years, and a growing number of laboratories around the world are able to closely replicate the development, right up to legal limits.
“We’re now technically at the point where these experiments are probably possible,” Rugg-Gunn said. “If the research continues, there is a very good chance that the new information will benefit health, particularly the understanding of the causes of recurrent miscarriage.”
Just after day 14, gastrulation occurs, a crucial step in which the embryo transforms from a simple ball of cells into three different layers of tissue that form a primitive body plan. “This is one of the most important steps in the entire development process, but this has never been examined or visualized before,” Rugg-Gunn said.
Implantation of the embryo into the lining of the uterus (endometrium) occurs between days six and 12, but the process continues after day 14 and can go wrong and is thought to be a common reason why IVF treatment does not work.
Prof Kathy Niakan, a developmental biologist at the University of Cambridge, said: “There’s an immunological interaction that’s really unique during that period of pregnancy. There’s a really interesting question about why in some cases maternal cells and fetal cells can’t coexist without some sort of attack or failure.”
In the third week, cells continue to differentiate and the first heart cells are formed. The majority of congenital heart defects are thought to occur 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 occurs because the neural tube does not close properly, but the exact steps have not been directly observed. Starting at about four weeks, scientists begin to obtain information about development from pregnancy scans and from embryos donated before termination of pregnancy.
Some argue that scientists may be exaggerating the potential clinical benefits of growing embryos beyond 14 days, questioning whether the ethical arguments supporting the legal limit have actually changed.
“Boundaries are meaningless if they don’t actually prevent you from doing something,” said Prof Anna Smajdor, a philosopher at the University of Oslo. “Now [scientists] They can do this, they don’t want to be limited. “The risk here is that the idea that these are moral landmarks that are the product of honest, moral deliberations with scientists will be ridiculed.”
It’s clearer now than it was in 1990 that an embryo doesn’t have a functional nervous system at 28 days old, but Smajdor says the ethics at play “necessarily ‘does it feel pain?'” “It cannot be reduced to the question,” he said. Even without a religious perspective, it is possible to think that embryos have a spiritual value because they have the potential to become human. “There is also a symbolic side to this.”
Others argue that responsibility changes with scientific advances. “Human embryos are a scarce and valuable resource,” said Sarah Norcross, chief executive of the charity Progress Educational Trust. “Is it right that scientists are legally obligated to stop studying these embryos in the laboratory after 14 days, when we can learn so much more from them and use that knowledge to better understand pregnancy loss and disease?”
Many believe that it is time to at least reopen the debate due to upcoming reforms to the law. “Just because there’s a debate doesn’t mean the rule will change,” Niakan said. “This means having an open, two-way dialogue about asking what can be gained, what the potential risks are, and how we feel about it.”