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Scientists are calling for a review of the 14-day rule for embryo research, saying extending the limit could help uncover the causes of recurrent miscarriages and congenital conditions.
Until now, scientists studying the earliest stages of life have been limited to growing embryos with a development time of up to fourteen days. A few weeks later they can pick up the development process again using pregnancy scans and material donated during a termination of pregnancy.
But this leaves a 'black box' period of two to about four weeks of development that has never been directly examined and which scientists say could be key to improving fertility treatments and understanding a variety of birth defects.
With an overhaul of fertility laws on the horizon and rapid scientific progress on the way, scientists are calling for an overhaul of the 14-day rule.
Dr. Peter Rugg-Gunn, from the Babraham Institute in Cambridge, said: "The period from two weeks to four weeks has been labeled the black box of embryo development. There is currently no practical way to study this, so our knowledge is really limited. Studying embryos beyond the 14-day limit could benefit patients. The sooner it can be allowed, the sooner patients can benefit from it in Britain."
Potential benefits include finding the causes of implantation failure, where the embryo fails to implant in the uterine lining, causing miscarriage, and the origins of congenital heart defects, which affect approximately one in 100 births and is estimated to responsible for approximately 40% of prenatal pregnancies. deaths.
"My view is that it is important that people understand what the benefits could be," added Rugg-Gunn, who stopped short of directly calling for an extension of the limit as part of sweeping proposals from the Human Fertilization and Embryology Authority ( HFEA). to modernize the law.
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The UK 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 the culture of embryos after 14 days of development or before the formation of the primitive streak (which forms the axis of the body) and was intended to balance the potential medical benefits of research with the special status of the human embryo.
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In 1990, however, the limit was theoretical, because scientists could not sustain embryo development in the laboratory for more than a few days. Over the past five years this has changed and a growing number of laboratories around the world are able to accurately replicate the development, up to the legal limit.
"We are now at the point where these experiments are probably technically possible," says Rugg-Gunn. "There is a very good chance that if the research could continue, the new knowledge would have health benefits, especially for understanding the causes of recurrent miscarriage."
Just after day 14, gastrulation occurs, a momentous step in which the embryo changes 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 all of development, but this has never been studied or visualized before," Rugg-Gunn said.
Implantation of the embryo into the uterine lining (endometrium) takes place between days six and twelve, but the process continues - and can go wrong - after day 14, and is considered a common reason why IVF treatment doesn't work.
Professor Kathy Niakan, a developmental biologist at the University of Cambridge, said: "There is an immunological interaction that is really unique during pregnancy. There is a very interesting question as to why, in some cases, the cells of the mother and the cells of the fetus cannot coexist without some form of attack or failure."
During the third week, the cells continue to differentiate and the first heart cells are formed. It is believed that a large proportion of congenital heart disease develops during this very early period of development. Between days 21 and 28, the neural tube (the embryonic precursor of the central nervous system) is formed and closed. Spina bifida is caused by the neural tube not closing properly, but the precise steps have not been directly observed. From around four weeks onwards, scientists begin to understand the development of pregnancy scans and embryos donated during abortion.
Some argue that scientists may overestimate the potential clinical benefits of growing embryos for longer than 14 days and question whether the ethical arguments underlying the legal limit have really changed.
"Borders are meaningless if they don't actually stop you from doing something," says Prof. Anna Smajdor, a philosopher at the University of Oslo. "Now [scientists] can do these kinds of things, they don't want to be limited. The risk is to make a mockery of the idea that these are moral cut-off points that are the product of honest, moral consultation 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 involved are "not necessarily reducible to 'does it feel pain?'. Even without a religious perspective, it is possible to think that embryos have moral value because they have the potential to become people. There is a symbolic component to it."
Others suggest that with scientific advances, responsibility has shifted. "Human embryos... are a scarce and precious resource," says 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 fourteen 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 legal reforms underway, it is at least time to reopen the debate. "Having the discussion does not mean the rule will change," Niakan said. "It means having an open, two-way dialogue about what can be gained, what the potential risks are and asking how we feel about that."