A unified developmental framework of the human placenta in its uterine environment in vivo and in vitro

Despite advances in single-cell profiling of the human placenta, the genetic programs governing its physiological remodeling throughout gestation remain incompletely understood; this limits the interpretation of trophoblast organoid models. Here, we reconstruct the human placenta in its uterine environment across gestation by integrating public single-cell data into a unified developmental framework developed through a specialized computational strategy. We resolve 100 cell subtypes, expanding the known cellular repertoire and uncovering extensive gestational dynamics. In the placental mesenchymal core, we define a stromal-vascular niche comprising previously unresolved fibroblast heterogeneity and vascular hierarchies (capillary, arterial, and venous). This niche undergoes reprogramming from early angiogenesis to vascular maturation at term and engages signaling programs that support villous homeostasis. Within the trophoblast lineage, we uncover differential progenitor dynamics: bipotent cytotrophoblast (CTB) progenitors persist throughout gestation, whereas extravillous trophoblast (EVT)-biased progenitors are almost absent at term, coinciding with differentiation into specialized states. Benchmarking trophoblast organoids against this reference shows distinct regional identities and developmental biases. Tissue-derived models recapitulate villous CTB whilst trophoblast stem cell-derived organoids resemble smooth chorion CTB; all models capture early gestational syncytiotrophoblast and progressive EVT differentiation. Together, this work provides a resource for understanding placental remodeling across gestation and guiding the use of in vitro models.