Endocrinology of Maternal-Placental Axis

Abstract

Pregnancy is a dynamic and complex state to which the mother’s physiology makes substantial adaptations that enable her to provide all the needs of the growing fetus. The placenta is a highly active, transient endocrine organ and a central regulator of maternal-placental-fetal physiology. It produces steroid and protein hormones, growth factors, and cytokines from precursor provided by the mother as well as by the fetus. Cytotrophoblasts secrete hypothalamic peptides and function in juxtaposition to syncytiotrophoblasts, which secrete the corresponding pituitary-like peptides in an anatomic arrangement analogous to the hypothalamic-pituitary axis. Some placental hormones play a predominant role at the beginning of pregnancy, favoring implantation and embryo development, while others exert their functions mainly in the second or third trimester, to maintain pregnancy and ensure appropriate fetal growth. Estrogens and progesterone are involved in pregnancy from before implantation to parturition. There are substances that are responsible of regulating maternal metabolic adaptation to pregnancy, in order to allow transfer of glucose and amino acids into the fetus. Many of these substances act in concert, in a complex interaction of hormones with one another, and in a fascinating cross talk between the placenta, the fetus, and the mother. The mechanisms involved in parturition are highly complex and involve endocrine factors, cytokines, oxytocin, and prostaglandins that lead the transition from a quiescent myometrium to a contractile state that allows delivery of the fetus. The endocrinology of the maternal-placental axis is still a progressive field of science, as some mechanisms are still incompletely understood.