Hormonal Changes in Pregnancy

Because of the time factor involved, it would be an impossible task to present the vast body of biochemical information accumulated during the last decade on the endocrine aspects of pregnancy. However, certain key points can be made concerning the feto-placental unit and the hormone levels and effects in normal gestation. These concepts will be discussed not merely for their academic value, but also as a base to evaluate our present diagnostic and therapeutic endeavors in obstetrical practice. With the audience's indulgence, an occasional personal conjecture will be interjected concerning hormonal mechanisms and clinical practices. Feto-Placental Unit. The fetus and the placenta are incomplete steroidogenic systems. They lack the capability of synthesizing all necessary steroidal hormones from more simple precursors in contrast to the ovaries, testes, and adult adrenal cortex. To complete the task a well-coordinated interdigitation of the synthetic capabilities of fetus, placenta, and mother is required. Since the mother is involved, one wonders whether the term "feto-maternoplacental unit" would not be more appropriate. First the fetal adrenal cortex and then the placenta will be discussed; hopefully, emphasizing the information which may have practical clinical significance. A. Adrenal Cortex. The fetal zone of the adrenal cortex persists only during gestation, constitutes about 80% of the gland, and is active in steroid metabolism. In the first trimester, it is believed this zone is primarily stimulated by human chorionic gonadotrophin (HCG); ACTH gaining prominence in control thereafter. The biochemical capabilities and limitations of the fetal adrenal cortex are shown in Fig. 1. Utilizing