Elevated levels of maternal IGF-I and IGF-binding proteins IGFBP-1 are regulated by placental hormones rather than pituitary control during pregnancy. Maternal IGF-I promotes fetal growth by stimulating nutrient transfer to fetus through placenta and IGFBP-1 suppresses fetal growth by inhibiting IGF-I binding to receptors in placenta. Since IGF-I and IGFBP-1 are produced in placenta and decidua, respectively, fetal growth is regulated by these substances in the locally formed paracrine system.