This study aims to evaluate the contribution of extraembryonic sources of serotonin to prefrontal cortex (PFC) development and understand the placental role and mechanisms of serotonin supplementation to the foetus. To this end, we used mice deficient in serotonin production (TPH1 and TPH2 KO) and serotonin transporters (SERT and OCT3 KO). We assessed serotonin levels in placenta and embryonic brain during different phases of prenatal neurodevelopment using HPLC and immunohistochemistry. Furthermore, we evaluated the PFC maturation and serotonergic wiring by 3D brain ECi imaging in these mice. Our results underlined major contributions of maternal, but not embryonic SERT and TPH1 to placental serotonin levels. The analysis of the morphological distribution in mouse placenta showed a high level of SERT in the syncytiotrophoblast layer of the chorionic area and OCT3 at the cytotrophoblast level. No signal for TPH1 was detected in placenta using immunostaining and in situ hybridization techniques. Furthermore, neither TPH1 nor TPH2 was detected in the placenta of mouse embryos by western blot. These data argue for a primary role of maternal platelet degranulation in fetal serotonin supplementation, rather than its production by the placenta. These data also suggest mechanisms of serotonin transport in the placenta: selective active transport by SERT across the placental barrier and passive non-specific transport by OCT3 within the areas of embryonic origin. These results shed light on a potential interference of selective serotonin reuptake inhibitors (SSRIs), the main family of antidepressant drugs prescribed during pregnancy, in serotonin supplementation of the embryo.