Pituitary Physiology During Pregnancy and Lactation

Abstract Pregnancy promotes a physiologic increase in the size of the maternal pituitary gland, especially the adenohypophysis, mainly due to estrogenic stimulation of lactotrophs. Prolactin promotes mammary gland differentiation and ensures milk production after delivery. Hyperprolactinemia inhibits gonadotrophin secretion. Placental growth hormone has a key role in the maternal adaptation, being closely related to fetal growth, and is a potential candidate to mediate insulin resistance observed in late pregnancy. Normal gestation is considered a state of hypercortisolism due to physiological activation of the hypothalamic-pituitary-adrenal axis. Although important changes in the physiology of the pituitary-thyroid axis occur, mainly due to the increase in chorionic gonadotrophin and thyroxin-binding globulin levels, the normal pregnant woman usually remains euthyroid. Gonadotrophin secretion is inhibited, preventing the stimulation of new ovarian follicles and, consequently, ovulation throughout the gestation period. The increase in antidiuretic hormone during pregnancy is balanced by placental vasopressinase activity, keeping plasma levels similar to that in nonpregnant subjects. Serum oxytocin concentrations gradually increase during gestation and reach peak values during labor. In conclusion, pregnancy is a state of integration of three complex and physiological neuroendocrine compartments: maternal, placental, and fetal. Each plays a critical role in maintaining the health of the embryo/fetus, placenta, and mother up to delivery.