05 March 2021 Vol 371, Issue 6533
Human embryo research beyond the primitive streak
By Insoo Hyun, Annelien L. Bredenoord, James Briscoe, Sigal Klipstein, Tao Tan
Science05 Mar 2021 : 998-1000 Restricted Access
It is time to revisit the “14-day limit”
Since the first successful birth resulting from in vitro fertilization (IVF) in the late 1970s, human embryo research has been subject to limits of time and developmental benchmarks. National guidelines, laws, and international norms have prohibited scientists from culturing embryos for research beyond 14 consecutive days, or beyond the appearance of a structure called the “primitive streak,” which defines the beginning of the formation of the principal tissues of the body and the end of the period when an embryo can divide into identical twins (1). At the time this limit was put in place 40 years ago, there were no methods to culture embryos in a dish for anywhere close to 14 days. But research since 2016 (2, 3) shows that it is likely possible to culture human research embryos past the 2-week limit and suggests that doing so will yield scientific insights that could prove important for human health and fertility (4). We thus urge policy-makers and the International Society for Stem Cell Research (ISSCR), which will soon release updated guidelines for stem cell and embryo research, to consider a cautious, stepwise approach to scientific exploration beyond the 14-day limit.