The hormonal changes and maternal adaptations of human pregnancy are among the most remarkable phenomena in nature. During pregnancy, the placenta, which is supplied with precursor hormones from the maternal-fetal unit, synthesizes large quantities of steroid hormones as well as various protein and peptide hormones and secretes these products into the fetal and maternal circulations. Near the end of pregnancy, a woman is exposed daily to ˜100 mg estrogen, 250 mg progesterone, and large quantities of mineralocorticoids and glucocorticosteroids. The mother, and to a lesser extent the fetus, are also exposed to large quantities of human placental lactogen (hPL), human chorionic gonadotropin (hCG), prolactin, relaxin, and prostaglandins and to smaller amounts of proopiomelanocortin (POMC) derived peptides such as adrenocorticotropic hormone (ACTH) and endorphin, gonadotropin-releasing hormone (GnRH), thyroid-stimulating hormone (TSH), corticotropin-releasing hormone (CRH), somatostatin, and other hormones.

Implantation, the maintenance of pregnancy, parturition, and finally lactation are dependent on a complex interaction of hormones in the maternal-fetal-placental unit. Moreover, there exists a complex regulation for the secretion of steroid hormones by means of protein and peptide hormones also produced within the placenta. In this chapter the discussion is focused on the hormones secreted by the placenta, the endocrinology of the fetus and the mother, the effect of various endocrine diseases on the maternal-fetal unit, and the use of endocrine tests to assess fetal well-being.