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Other scientists have already used human stem cells to create a “blastoid, ” a structure mimicking a pre-embryo, that can serve as a research alternative to a real one.

Scientists are using human stem cells to create a structure that mimics a pre-embryo and can serve as a research alternative to a real one.

But it’s possible to ask whether a pre-embryo’s genetic uniqueness, or its potential to grow into a human being, sets it apart from other tissues.

According to European Union regulations, a pre-embryo is considered tissue: it must be handled, stored, and transported according to a 2004 directive that also addresses bone marrow for transplants and skin for grafts.

Conception, artificial or otherwise, is so uncertain that each pre-embryo, once it’s implanted, has only a one-in-three chance of growing into a human being.