3D post-implantation co-culture of human embryo and endometrium.

Embryo-maternal interaction is essential for post-implantation human development. While endometrial organoids have enabled in vitro modeling of the uterine environment, a fully integrated 3D co-culture system with human embryos has not been established. Here, we develop a physiologically relevant 3D platform that supports the co-culture of human embryos with endometrial organoids, enabling reciprocal embryo-maternal communication. This system sustains development to day 14 post-fertilization with structural and molecular fidelity to Carnegie stage landmarks, including yolk sac formation, primordial germ cell specification, and trophoblast maturation. Single-cell transcriptomics and functional assays reveal that the endometrial niche accelerates extravillous trophoblast emergence at day 9 post-fertilization and primes their invasive programs. Disruption of maternal signals, including human chorionic gonadotropin signaling blockade, markedly impairs embryonic progression. This co-culture system provides a powerful and tractable model to dissect human peri- and post-implantation development, with broad relevance to early pregnancy loss, placental biology, and reproductive medicine.