Manipulating embryogenesis and testing for potential: two real problems for the regulation of stem cell-based embryo models.

Stem cell-based human embryo models (SCBEMs), generated in vitro from stem cells, currently exist outside the scope of regulatory frameworks that govern in vitro embryo research in most jurisdictions. A widely discussed proposal suggests using a 'Turing test' framework, whereby regulatory oversight is triggered if an SCBEM is found to be 'equivalent' to a human embryo. In this paper, we argue that such a proposal faces two major complications. First, sophisticated laboratory techniques such as trophoblast replacement allow researchers to manipulate normal embryogenesis, obscuring whether a given SCBEM meets embryo-like regulatory thresholds. Second, attempts to assess SCBEMs' developmental potential-especially through non-human analogues-rest on tenuous epistemic assumptions that may not align with human-specific developmental trajectories. Given SCBEMs' potential manipulability and uncertain biological and potentiality benchmarks, we argue that reliance on equivalence-based frameworks alone is highly problematic. We conclude by urging a cautious, flexible approach that recognises both the scientific promise of SCBEMs and the normative need to prevent the circumvention of regulatory safeguards.