Obstetrics and Gynecology - A.M. Hromova 2000

Changes in the woman's body during pregnancy
Changes in the female endocrine system during pregnancy

Pregnancy is a physiological process in the female body accompanied by adaptive and compensatory Changes in the functioning of all Organs and systems, as well as an intensification of metabolic processes. These changes often border on pathology, yet their purpose is to adequately meet the growing demands

of the fetus, adapt the pregnant woman's body to operating under the conditions of a third (fetal) circulatory loop, and prepare for childbirth.

A crucial role during pregnancy is played by the establishment of a new endocrine balance within the body. From the moment the fertilized ovum implants into the uterine wall and the trophoblast forms, the latter begins to synthesize human chorionic gonadotropin (hCG). Owing to the luteotropic effect of hCG, the menstrual corpus luteum in the Ovaries transforms into the corpus luteum of pregnancy. It is capable of synthesizing progesterone and estrogenic Hormones (primarily estrone and estradiol). The corpus luteum persists throughout gestation, with its peak activity observed at 4–5 weeks of gestation.

Beginning in the 3rd month of the gestational process, degenerative changes occur in the corpus luteum of pregnancy, and from this point onward, its function is assumed by the Placenta. As an endocrine organ, the placenta operates within a unified uteroplacental-fetal system.

The placenta (syncytiotrophoblast, cytotrophoblast, and decidua) produces hormones of both protein and steroid nature. The level of estrogenic hormones rises significantly from the onset of active placental function (at 13 weeks of gestation) and continues to increase progressively throughout the entire pregnancy. This occurs because, against the backdrop of enhanced synthesis of estrone and estradiol in the maternal ovaries, there is also an increase in the level of estriol produced by the fetoplacental complex. Furthermore, 90% of it is formed in the fetal Liver from dehydroepiandrosterone produced by the fetal Adrenal Glands, and only 10% in the placenta from maternal precursors (estrone and estradiol). The steadily increasing concentration of estrogens ensures the GROWTH AND DEVELOPMENT of the Uterus, regulates biochemical processes in the myometrium, increases The activity of enzymatic systems, intensifies METABOLISM/26.html">Energy Metabolism, and promotes the accumulation of Glycogen and ATP necessary for fetal development.

Changes in the qualitative composition of estrogens occur during the period of preparation for and development of labor activity: the fractions of the most active labor-inducing agents (estradiol and estriol) increase. An equally important steroid hormone is progesterone, which prepares the body for pregnancy and ensures its normal course. This is due to the hormone's ability to inhibit uterine contractile activity, maintain the tone of the isthmic-cervical segment, and stimulate the growth of the uterus and Blood Vessels during pregnancy. The level of progesterone increases especially after 12 weeks of pregnancy, rising 10- to 20-fold by the end of gestation.

In addition to Steroids, the placenta synthesizes about 10 protein hormones, among which human chorionic gonadotropin and placental lactogen are of the greatest importance.

Human chorionic gonadotropin is produced by the cytotrophoblast throughout pregnancy, with peak production occurring During the first 10 weeks. It is precisely during this time that the corpus luteum of pregnancy Functions actively, and supporting its development is The primary function of chorionic gonadotropin.

From the 12th week and throughout the entire gestation period, The production of placental lactogen increases; it plays a specific role in pulmonary surfactant production and fetoplacental osmoregulation. Placental lactogen is a polypeptide hormone possessing lactogenic, somatotropic, and luteotropic activity. Its primary role is to regulate carbohydrate and Lipid Metabolism and enhance Protein Synthesis in the fetal body. This hormone is produced by the syncytiotrophoblast of the placenta starting at 5–6 weeks of pregnancy. Ninety percent of placental lactogen enters the pregnant woman's blood, and 10% enters the Amniotic Fluid. Throughout gestation, the concentration of placental lactogen gradually increases, reaching its maximum level at 36–37 weeks of pregnancy. Thereafter, the hormone level stabilizes until 39 weeks and subsequently declines. Following childbirth, placental lactogen rapidly disappears from the maternal blood.

An important role in the physiological functioning of the mother-placenta-fetus system is played by Prostaglandins (especially E₂ and F_2α). They are not considered true hormones per se, as they are not secreted by Endocrine glands but are instead synthesized by all body Tissues. However, these BIOLOGICALLY ACTIVE SUBSTANCES are capable of enhancing or weakening the Action of Hormones on target Cells. By regulating The Biosynthesis of cyclic adenosine monophosphate within them, endogenous prostaglandins influence almost all Links of the Reproductive System, including sperm activity in cervical mucus, ovulation and steroidogenesis processes in the ovaries, ovum implantation, the course of pregnancy, the induction and Regulation of Labor Activity, and Lactation.

The endocrine activity of the ovaries and the fetoplacental complex determines a new operational mode for the central endocrine glands. Under The Influence of continuous impulse activity from the Cerebral Cortex, hypothalamic activity increases, leading to an enhanced synthesis of releasing factors for pituitary tropic hormones and neurohormones (Vasopressin and Oxytocin). Vasopressin participates in The regulation of volumo-osmotic Homeostasis, activates the function of the fetal Hypothalamus, and influences corticotropin secretion. The level of this hormone depends to a certain extent on estrogenic stimulation; it is somewhat decreased in the first weeks of pregnancy and then rises markedly. Oxytocin increases myometrial activity and stimulates mammary gland cells, making it crucially important for the induction of labor, the course of childbirth, and the maintenance of normal lactation during the postpartum period. In addition to its uterotonic action, it possesses moderate vasopressor and antidiuretic activity and slightly increases the aggregation of formed blood elements. By the time of delivery, the concentration of oxytocin in the maternal blood reaches its maximum level. However, it has been established that even during this period, the oxytocin content in the fetoplacental system is significantly higher than in the maternal Circulation, which indicates the involvement of the fetal hypothalamo-pituitary system in preparing the pregnant woman's body for labor.

Notable histological and functional changes also occur in the activity of the adenohypophysis. Within the very first 3 months of pregnancy, the synthesis of luteinizing hormone and prolactin increases. The latter prepares the Mammary Glands for lactation, and the steady increase in its blood levels with advancing gestation is explained by the stimulating action of abundant Steroid Hormones, especially estrogens.

In parallel, the pituitary production of tropic hormones (FSH, LH, ACTH, TSH, GH) increases, which, via a positive feedback mechanism, stimulates peripheral endocrine glands to secrete the respective hormones required under conditions of intensified metabolism and fetal growth. The adrenal cortex is closely linked to ACTH levels, leading to its hypertrophy during pregnancy and associated pronounced functional changes. The synthesis of glucocorticoids, which regulate carbohydrate, protein, and lipid metabolism, increases substantially, accounting for the hyperlipidemia and hypercholesterolemia characteristic of pregnancy. The level of mineralocorticoids—primarily aldosterone—constantly rises; by enhancing sodium reabsorption and potassium excretion in the collecting tubules of the renal cortex, it plays a vital role in regulating Water-electrolyte balance. Under the influence of large amounts of sex steroids, which reduce vascular sensitivity to vasopressor substances, the function of The adrenal medulla is compensatorily activated, resulting in enhanced catecholamine biosynthesis and elevated blood levels of adrenaline and noradrenaline.

As pregnancy progresses, thyroid function becomes activated, and the synthesis of its hormones is upregulated. The quantity of bound forms of THYROID HORMONES increases to a greater extent, while the levels of free, active fractions of thyroxine and triiodothyronine remain comparable to pre-pregnancy values. The primary role of thyroid hormones is metabolic, consisting of enhanced utilization of oxygen and ATP and the activation of protein synthesis, which is extremely important for the normal modulation of fetal growth and development. As pregnancy progresses, the synthesis of thyrocalcitonin increases. This hormone exists in a dynamic antagonistic equilibrium with the parathyroid hormone, which accounts for the decreased activity of the Parathyroid glands during pregnancy. Consequently, the parathyroid hormone level drops as pregnancy advances, causing disruptions in phosphorus-calcium metabolism, which explains the potential onset of hypocalcemia and Muscle cramps.

Certain changes are also established in pancreatic activity. Beginning In the second trimester of pregnancy, Insulin production increases, which is necessary to maintain maternal blood glucose levels under conditions of pronounced Carbohydrate Metabolism intensification driven by the steadily rising energy demands of the fetus. Thus, the function of nearly all endocrine glands increases, establishing a new endocrine balance to ensure the normal course of pregnancy.