Disrupted placental serotonin synthetic pathway and increased placental serotonin: Potential implications in the pathogenesis of human fetal growth restriction

•Serotonin (5-HT) pathway is important for feto-placental growth.•5-HT pathway is important for fetal growth across gestation.•The components of placental 5-HT pathway are altered in fetal growth restriction (FGR).•The activity of placental 5-HT synthetic enzyme is increased in FGR.•Placental 5-HT content is increased in FGR.