Gist Croft, Alessia Deglincerti, Ali H. Brivanlou/ The Rockefeller University via AP
This microscope photo provided by The Rockefeller University shows a human embryo 12 days after fertilization in vitro, with different cell types marked by separate colors.

Researchers grow human embryos outside of womb for 13 days. Ethical?

Researchers kept human embryos alive in a laboratory for a record 13 days, a breakthrough which sheds light on the question of how long such experiments should last.

Scientists studying the development of human embryos in a laboratory setting have succeeded in growing the organisms for nearly two weeks outside of a human womb, allowing for new insights into the early stages of human life.

"We will learn things we cannot even imagine," Rockefeller University embryologist Ali Brivanlou told NPR. "It's as if you say: 'If I look at new sets of Hubble Space Telescope pictures that I haven't seen yet, what will I learn from them?' It's difficult to say until you look at them."

The scientists' in vitro breakthroughs appeared Wednesday in two journals: Nature and Nature Cell Biology.

The 13-day analytical period following the embryos’ fertilization broke the previous span of nine days for such research in a lab. But such advances also raise ethical questions concerning the status of the early-stage humans and how long study of the growing organisms should last.

Still, scientists are excited because they believe new information gleaned past the point of the previous standard  – one week – could help them better understand such areas as in vitro fertilization, miscarriages, birth defects, cellular engineering, and regeneration.

"It actually allows us to understand the very first steps in our development at the time of implantation where the embryo, really for the first time, reorganises itself to form the future body," University of Cambridge mammalian development and stem cell biology professor Magdalena Zernicka-Goetz, one of the study's authors, told the BBC. "Those steps we didn't know before so it has enormous implication for reproductive technologies."

While doctors and researchers may be enthused, this breakthrough also draws ethical scrutiny. The 13-day limit on embryos living in a petri dish outside the womb was not a result of scientists' inability to continue their study, but their reluctance to go any further. International regulations do not allow for the study of embryos more than two weeks after fertilization due to embryos' transition to the gastrulation phase, in which the basic body plan develops.

But 14 days is a limit that some view as too restrictive, given the potential benefits further exploration could provide. 

"Longer cultures could provide absolutely critical information for basic human biology," Dr. Zernicka-Goetz told reporters in London. "But this would of course raise the next question – of where we should put the next limit."

"Now that it has become possible to culture human embryos to the 14-day limit and perhaps beyond, the time is right for the scientific community to educate the public about the potential benefits and to work with regulators on ethical consensus to guide this important research," Rockefeller University associate vice president Amy Wilkerson said in a release on the findings.

The arguments to limit such research are similar to those surrounding stem cell research, cloning, and abortion: Life begins at conception – and this type of research violates the sanctity of human life. Scientists, opponents say, are essentially creating and then killing a "human" in the name of medical advances. The argument revolves around when "life" begins.

"[I]f we do not use a 14 day rule, what limit will we use? Twelve weeks or so as in many European abortion laws? Viability (at around 23 weeks) as in U.S. abortion law? Human development is a seamless process, but ultimately lines need to be drawn even when — especially when — they do not naturally exist," wrote Henry Greely, Director, Center for Law and the Biosciences; Professor (by courtesy) of Genetics, Stanford School of Medicine in a statement to the Genetic Experts News Service. "I do not see a politically, or, for most people, morally acceptable line after 14 days. Given the questionable scientific value of the research, no case has been made for even revisiting the line, let alone changing it."

The traditional boundary, which some view as arbitrary, is close to the beginning stages of the "primitive streak" one of the first established markers of early symmetrical bodily construction - and, significantly, an embryo's first major step toward becoming a person.

"The 14-day rule has kept it pretty limited in terms of what scientists could do. Once that goes, then it begins to sort of say: 'It's open season on human embryos. Anything goes'," University of Chicago bioethicist Daniel Sulmasy told NPR.

"The question has to be: 'Are there any limits to what we will do to human beings in order to gain scientific knowledge?' And then who counts as a human being?" he added.

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