We know more about the embryos of mice and fruit flies than we do about human embryos, due to old restrictions that also could be slowing the advance of biomedicine. Back in 1979, a bioethics board commissioned by the United States Department of Health, Education, and Welfare recommended that scientists not conduct research on human embryos with a gestational age greater than 14 days. Five years later, a similar committee endorsed the same idea in the United Kingdom, and this has led to guidelines and formal rules in many countries limiting embryo research to the very early stages. Restrictions vary from country to country and do not always draw the line precisely at 14 days, but rather at the beginning gastrulation, when an early stage of cells called a blastula reorganizes into what’s called a gastrula. Some countries, including Canada, Australia, New Zealand, and a few European nations, have formal restrictions on what can be done, even during the first 14 days of embryonic life, but recent advances in embryo science are challenging the wisdom of the 14-day stopping point.
Gastrulation was an arbitrary cutoff point, chosen to carve out a research period for scientists. 38 years ago, it wasn’t expected to be a ‘limit’, because there was no technical capability to maintain human embryos in vitro (in laboratory conditions, outside the womb) more than a few days into gestation. Rather, it was chosen as a compromise between research interests and societal worries resulting from the influence of organized religion. Not long after the 1979 recommendation, however, scientists were realizing that appearance of what’s called the primitive streak, which signifies the start of gastrulation, does represent a kind of change in an embryo’s condition. Notably, this is the point after twinning and fusion cannot occur. Twinning is when an early embryo splits into two or more embryos, each of which then can develop into an infant. Fusion is when two or more embryos combine into one.
The idea that the number of people resulting from fertilization of human eggs is set after formation of the primitive streak resonated with members of some religions. They equated it with “ensoulment”, a belief that a nonphysical entity called a soul enters a developing child at a certain point. Christians believe that such a soul is created at that point, while Hindus believe that it has moved from another animal that has just died, and is thus reincarnated.
But, there is no rule in any major religion that gives moral status to an embryo at 14 days gestation. For Catholics and Christian fundamentalists, personhood begins at fertilization, so socially-conservative politicians try to increase restrictions as close as possible to fertilization, whether in connection with research or abortion. For everyone else though, a 14 limit is way too early, firstly because the number of secular people with no religion is high and growing in North America, Australia, New Zealand, and especially in Western Europe. Second, moral status early in the embryonic period is out of sync with non-Christian religions and even with many Christian sects. Hinduism considers the embryo to be a person, but India allows abortion through the 20th week, and Buddhists societies have similar views. Islam gives moral status only from 120 days gestational age, which is far into the fetal period, while Judaism also looks at human development in terms of a progression. In the Babylonian Talmud, an embryo is “like water”, having no status, until 40 days gestation. At this point, the developing human gets a kind of legal status, but not personhood until the head crowns at birth.
So, really there’s no societal basis for a 14-day limit, and, by the way, research utilizes leftover embryos from fertility clinics, embryos that would be discarded anyway. Upon reaching 14 days gestation, a human embryo in research also must be discarded, so research is not something that ever comes into conflict with an embryo developing into an actual human baby.
Unlike 1979, today, human embryos can be maintained in vitro up through 13 days gestation. Scientists see no technical obstacle against longer times, but the 14-day guidelines prevent them from trying. Why might they want to try? One potential benefit is that we could learn more about what causes unsuccessful pregnancies. Most fertilized eggs end up as spontaneous abortions, usually so early in gestation that the mother never knew that she was pregnant. Others abort naturally a little bit later; these are what are commonly called miscarriages.
Studying human embryos in vitro also would speed progress toward an artificial womb. Finally, we would learn faster how to create all kinds of replacement body tissues that could cure degenerative diseases, possibly even including old age. We’ll examine some of these embryo-related treatments in future posts.