Hum Reprod Open. 2026 ;2026(2):
hoag028
BACKGROUND: Although assisted reproductive technologies have enabled millions of births worldwide, in vitro embryo culture systems remain a simplified and static approximation of the highly dynamic environment of the female reproductive tract. Commercial culture media lack many of the biochemical, biophysical, and temporal features of oviductal and uterine fluids, including hormonally regulated secretions, extracellular vesicles, and epithelial-derived signaling cues. These limitations are increasingly linked to altered embryonic programming, suboptimal implantation, and subtle but persistent effects on perinatal and long-term health outcomes.
OBJECTIVE AND RATIONALE: This review critically examines how reproductive tract-derived factors and advanced three-dimensional (3D) in vitro models can improve the physiological relevance of embryo culture systems in human ART. We focus on the biological roles of native reproductive fluids and extracellular vesicles and the emerging contribution of reproductive tract organoids and assembloids as sources of defined, stage-specific secretomes capable of bridging the gap between artificial and in vivo-like conditions.
SEARCH METHODS: A comprehensive literature search was conducted in PubMed, Scopus, and Web of Science for studies published up to March 2026 using terms related to embryo culture media, reproductive fluids, extracellular vesicles, organoids, implantation, and human IVF. Evidence from human studies and relevant animal models was included to provide mechanistic insight and translational context, with emphasis on experimental approaches directly informing ART practice.
OUTCOMES: Reproductive tract fluids contain complex mixtures of proteins, metabolites, lipids, and extracellular vesicles that regulate fertilization, early embryonic development, epigenetic programming, and maternal-embryo communication. While supplementation of embryo culture media with native fluids improves embryo quality and developmental competence in multiple species, clinical translation is constrained by donor variability, biosafety concerns, and limited standardization. Reproductive tract 3D cell cultures represent a promising complementary approach, as they can recapitulate key aspects of epithelial architecture, hormonal responsiveness, and secretory activity under controlled conditions. Organoid-derived secretomes, including extracellular vesicle cargo, have been shown to support reproductive processes such as sperm viability, trophoblast function, immune modulation, and endometrial receptivity. Moreover, advances in epithelial-stromal assembloids and microengineered platforms further enhance physiological fidelity by partially restoring multicellular interactions relevant to implantation-related signaling. However, these systems also present important limitations, including variability between lines, incomplete cellular complexity, scalability challenges, and unresolved regulatory considerations for clinical translation.
LIMITATIONS REASONS FOR CAUTION: This review is based on heterogeneous evidence derived from both human and animal studies, which may limit direct clinical translation due to species-specific differences in reproductive physiology and embryo development. Variability in experimental design, culture conditions, and reporting standards across studies introduces potential bias and complicates comparative interpretation. In particular, the use of reproductive fluids is subject to significant inter- and intra-donor variability, differences in collection and processing methods, and incomplete biochemical characterization, all of which represent important confounding factors. Similarly, organoid and assembloid models exhibit variability between lines, incomplete cellular complexity, and differences in differentiation state, which may influence secretome composition and functional outcomes. Moreover, many studies have relied on surrogate endpoints, such as embryo morphology or blastocyst formation, rather than long-term clinical outcomes, limiting conclusions regarding safety and efficacy in human ART.
WIDER IMPLICATIONS: Organoid- and assembloid-derived secretomes represent a scalable, ethically sustainable, and mechanistically tractable strategy to advance biomimetic embryo culture in human ART. These systems provide a framework for defining biologically relevant secretory profiles, enabling stage-specific and, potentially, patient-informed supplementation strategies. Integrating reproductive tract organoid technologies with extracellular vesicle biology and dynamic culture platforms may ultimately improve embryo competence, implantation success, and long-term offspring health, while supporting safer and more physiologically informed ART practices.
STUDY FUNDING/COMPETING INTERESTS: This work was funded by the Ministerio de Ciencia e Innovación and the Agencia Estatal de Investigación (MICIU/AEI/10.13039/501100011033) under grant numbers PLEC2022-009246, PID2023-148535OB-I00, and CNS2022-135933; the European Social Fund (ESF), Investing in Your Future; and the Fundación Ramón Areces. N.H.-D. is supported by a Marie Curie PhD fellowship from the AFRODITA Doctorate Network, funded by the HE programme under the MSCA-DN grant agreement No. 101120126. None of the authors have a conflict of interest to disclose.
Keywords: ART; biomimetic systems; embryo culture media; endometrial organoids; endometrial receptivity; extracellular vesicles; human IVF; implantation failure; oviductal organoids; reproductive fluids