Embryo models need consistent ethical oversight

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).