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What Is a SHEEF, and Why Should We Care?

April 28, 2017 • Posted in Blog

D. Joy Riley, M.D., M.A. Executive Director

Human embryo research has long been guided by what is known as the “14-day rule.” That is, various nations have allowed research on embryos up to 14 days post fertilization. The 14-day rule was put in place ostensibly in order to avoid causing pain for the developing embryo. The primitive streak — the first visible evidence of gastrulation and the formation of differentiated tissues in the embryo — appears at about day 15 after fertilization. (See video at the bottom of this post for more information.)

When the 14-day rule was put in place, laboratories were more