Studies of stem-cell-derived models of human embryos can uncover obscure developmental events that cause pregnancies to fail. Studying ‘non-integrated’ models, which lack extra-embryonic lineages required to make an embryo biologically complete, can seem to pose fewer ethical challenges than do integrated models, which contain embryonic and extra-embryonic lineages (Nature 622, 469–470; 2023).
Competing Interests
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M.Z-G. holds patents to build stem-cell-derived embryo models.