The placenta is a fetal endocrine organ that secretes many neuroactive factors, including steroids, that play critical roles in brain development. The study of the placenta-brain axis and the links between placental function and brain development represents an emerging research area dubbed "neuroplacentology." The placenta drives many circulating fetal steroids to very high levels during gestation. Recent studies have highlighted the critical role of placental steroids in shaping specific brain structures and behaviors. This review uses a cross-species framework to discuss the genomic factors, in-utero environmental changes, and placental conditions that alter placental steroidogenesis, leading to changes in early developmental trajectories relevant for psychiatric conditions such as autism, in a sex-linked manner.