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takyon writes:

Scientists have developed a way to keep embyros alive outside of a womb for days longer than before, by using a mix of amino acids, hormones, and growth factors:

Zernicka-Goetz says being able to go past the previous limit is "extremely important" from a scientific point of view. That's because the seventh day of development is the time when the human embryo becomes embedded within the body of the mother — when it becomes implanted in the womb. Scientists had thought embryos could only keep developing if they were safely in the womb and receiving instructions from the mother's body.

But the embryos in the studies implanted in the dish like they they would in the womb. Then they started organizing themselves into the very early stages of different complex organs and tissues and structures in the body, the researchers report.

A commentary accompanying the research urges regulators to revisit the "14-day rule":

In principle, these two lines of research could lead to scientists being able to study all aspects of early human development with unprecedented precision. Yet these advances also put human developmental biology on a collision course with the '14-day rule' — a legal and regulatory line in the sand that has for decades limited in vitro human-embryo research to the period before the 'primitive streak' appears. This is a faint band of cells marking the beginning of an embryo's head-to-tail axis. The 14-day rule has been effective for permitting embryo research within strict constraints — partly because it has been technologically challenging for scientists to break it. Now that the culturing of human embryos beyond 14 days seems feasible, more clarity as to how the rule applies to different types of embryo research in different jurisdictions is crucial. Moreover, in light of the evolving science and its potential benefits, it is important that regulators and concerned citizens reflect on the nature of the restriction and re-evaluate its pros and cons.

Self-organization of the in vitro attached human embryo (DOI: 10.1038/nature17948)

Self-organization of the human embryo in the absence of maternal tissues (DOI: 10.1038/ncb3347)

Original Submission