Serotonin is another possible mediator of programming effects induced by prenatal stress on the offspring's neurocognitive and behavioural development. During gestation, serotonin acts as a trophic factor regulating cell division, differentiation and synaptogenesis . Animal studies have shown that increased serotonin exposure during gestation is associated with alterations in many neuronal processes and subsequent changes in offspring behaviour. Recent work has identified an endogenous serotonin biosynthetic pathway in the human placenta , suggesting a possible role for alterations in placental serotonin in human fetal