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This report is part of a series examining the ethical, policy and scientific issues that arise in the controversial field of human embryo research. A list of acronyms used is available here.

Introduction

The guideline limiting human embryo research in vitro to 14 days post fertilization (dpf)—generally known as the 14-day rule—is widely accepted by many governments, foundations, and nongovernmental organizations (NGOs) interested in human embryo research. In several countries such as the United Kingdom, research on embryos beyond 14 dpf is illegal (Matthews and Gallego Marquez 2019). However, in the United States where human embryo research with federal funds is banned, there are no laws prohibiting scientists from conducting research on embryos beyond 14 dpf using nonfederal funding. This deadline is thus not a legal rule but a voluntary guideline recommended by scientific and medical societies, including the International Society for Stem Cell Research (ISSCR 2016), the National Academies of Science, Engineering, and Medicine (NASEM 2010), and the Association for Reproductive Medicine (ASRM 1986). In practice, however, U.S. scientists are reluctant to violate the 14-day guideline.

Until recently, concerns about the deadline were simply theoretical because the technical capacity to conduct research on embryos beyond the 14-day limit did not exist. That changed in 2016 when two research groups were able to culture embryos in vitro up to 14 days, at which point they ended experiments to avoid violating the 14-day rule (Shahbazi 2016; Deglincerti et al. 2016). This newly developed technical capacity has led some commentators to contemplate the pros and cons of a possible extension of the 14-day guideline (Harris 2016; Hyun, Wilkerson, and Johnston 2016; Pera 2017; Warnock 2017). Two new questions have thus arisen: Should the guideline be changed? If so, what should replace it? These questions have scientific, policy, and ethical dimensions.