Pregnancy from implantation: clinical utility and residual ambiguity in reproductive terminology

The 2025 International Glossary on Infertility and Fertility Care defines pregnancy as 'a state of reproduction beginning with implantation of an embryo and ending with the complete expulsion and/or extraction of the products of implantation'. This implantation-based definition is clinically useful, particularly for assisted reproductive technology ART, registries and outcome reporting. However, it also leaves a biologically relevant interval - between fertilization and implantation - outside the term 'pregnancy'. This interval is not a semantic void: it includes fertilization, cleavage, blastocyst formation, embryo-maternal signalling in vivo, and embryo culture in vitro. This commentary will argue that the Glossary would benefit from a more explicit distinction between pregnancy as an implantation-dependent clinical state, and post-fertilization preimplantation embryonic development as a biological phase. Such clarification would not require abandoning implantation-based definitions for clinical reporting, but would reduce ambiguity in counselling, reproductive pharmacology, ethics and public communication. A stage-specific terminology may better serve both scientific precision and transparent discussion of interventions that act before fertilization, after fertilization but before implantation, or after implantation.