Functional mother-placenta-fetus system

According to modern concepts, the unified mother-placenta-fetus system that arises and develops during pregnancy is a functional system. According to the theory of P.K. Anokhin, a functional system is considered to be a dynamic organization of the body's structures and processes, which involves individual components of the system regardless of their origin. This is an integral formation that includes central and peripheral links and operates on the principle of feedback. Unlike others, the mother-placenta-fetus system is formed only from the beginning of pregnancy and ends its existence after the birth of the fetus. It is the development of the fetus and its gestation until the due date that is the main purpose of the existence of this system.

The functional activity of the mother-placenta-fetus system has been studied for many years. At the same time, individual links of this system were studied - the state of the mother's body and the adaptation processes in it that occur during pregnancy, the structure and functions of the placenta, the processes of growth and development of the fetus. However, only with the advent of modern methods of lifetime diagnostics (ultrasound, Doppler ultrasound of blood circulation in the vessels of the mother, placenta and fetus, careful assessment of the hormonal profile, dynamic scintigraphy), as well as the improvement of morphological studies, it was possible to establish the main stages of the establishment and principles of functioning of a single fetoplacental system.

The features of the emergence and development of a new functional system mother-placenta-fetus are closely related to the features of the formation of a provisional organ - the placenta. The human placenta belongs to the hemochorial type, characterized by the presence of direct contact between the mother's blood and the chorion, which contributes to the most complete implementation of complex relationships between the organisms of the mother and the fetus.

One of the leading factors ensuring the normal course of pregnancy, growth and development of the fetus are hemodynamic processes in the single mother-placenta-fetus system. The restructuring of the hemodynamics of the mother's body during pregnancy is characterized by the intensification of blood circulation in the vascular system of the uterus. The blood supply to the uterus with arterial blood is carried out by a number of anastomoses between the arteries of the uterus, ovaries and vagina. The uterine artery approaches the uterus at the base of the broad ligament at the level of the internal os, where it divides into ascending and descending branches (first order), located along the ribs of the vascular layer of the myometrium. From them, 10-15 segmental branches (second order) depart almost perpendicular to the uterus, due to which numerous radial arteries (third order) branch off. In the main layer of the endometrium, they are divided into basal arteries supplying blood to the lower third of the main part of the endometrium, and spiral arteries that go to the surface of the mucous membrane of the uterus. The outflow of venous blood from the uterus occurs through the uterine and ovarian plexuses. The morphogenesis of the placenta depends on the development of the uteroplacental circulation, and not on the development of the circulation in the fetus. The leading role in this is given to the spiral arteries - the terminal branches of the uterine arteries.

Within two days after implantation, the fragmenting blastocyst is completely immersed in the uterine mucosa (nidation). Nidation is accompanied by trophoblast proliferation and its transformation into a two-layer formation consisting of cytotrophoblast and syncytial multinuclear elements. In the early stages of implantation, the trophoblast, not possessing pronounced cytolytic properties, penetrates between the cells of the surface epithelium, but does not destroy it. The trophoblast acquires histolytic properties during contact with the uterine mucosa. Destruction of the decidual membrane occurs as a result of autolysis caused by the active activity of uterine epithelium lysosomes. On the 9th day of ontogenesis, small cavities - lacunae - appear in the trophoblast, into which the mother's blood flows due to the erosion of small vessels and capillaries. The trophoblast cords and partitions separating the lacunae are called primary. By the end of the 2nd week of pregnancy (12-13th day of development), connective tissue grows into the primary villi from the chorion side, resulting in the formation of secondary villi and intervillous space. From the 3rd week of embryonic development, the period of placentation begins, characterized by vascularization of the villi and the transformation of secondary villi into tertiary villi containing vessels. The transformation of secondary villi into tertiary villi is also a critical period in the development of the embryo, since gas exchange and transport of nutrients in the mother-fetus system depend on their vascularization. This period ends by the 12-14th week of pregnancy. The main anatomical and functional unit of the placenta is the placenta, the component parts of which are the cotyledon on the fetal side and the curuncle on the maternal side. The cotyledon, or placental lobule, is formed by the stem villus and its numerous branches containing fetal vessels. The base of the cotyledon is fixed to the basal chorionic plate. Individual (anchor) villi are fixed to the basal decidua, but the vast majority of them float freely in the intervillous space. Each cotyledon corresponds to a certain section of the decidua, separated from the neighboring ones by incomplete partitions - septa. At the bottom of each curuncle, spiral arteries open, supplying blood to the intervillous space. Since the partitions do not reach the chorionic plate, individual chambers are connected to each other by the subchorionic sinus. From the side of the intervillous space, the chorionic plate, like the placental partitions, is lined with a layer of cytotrophoblast cells. Due to this, the maternal blood does not come into contact with the decidua in the intervillous space. The placenta formed by the 140th day of pregnancy contains 10-12 large, 40-50 small and 140-150 rudimentary cotyledons. At the indicated time, the thickness of the placenta reaches 1.5-2 cm, further increase in its mass occurs mainly due to hypertrophy.At the border of the myometrium and endometrium, the spiral arteries are supplied with a muscular layer and have a diameter of 20-50 μm; after passing the main plate, when entering the intervillous space, they lose muscular elements, which leads to an increase in their lumen to 200 μm or more. The blood supply to the intervillous space occurs on average through 150-200 spiral arteries. The number of functioning spiral arteries is relatively small. During the physiological course of pregnancy, the spiral arteries develop with such intensity that they can provide blood supply to the fetus and placenta 10 times more than necessary; their diameter by the end of pregnancy increases to 1000 μm or more. Physiological changes that the spiral arteries undergo as pregnancy progresses include elastolysis, degeneration of the muscular layer and fibrinoid necrosis. Due to this, peripheral vascular resistance and, accordingly, blood pressure decrease. The process of trophoblast invasion is completely completed by the 20th week of pregnancy. It is during this period that systemic arterial pressure decreases to its lowest values. There is virtually no resistance to blood flow from the radial arteries to the intervillous space. Blood outflow from the intervillous space is carried out through 72-170 veins located on the surface of the terminal villi and, partly, into the marginal sinus bordering the placenta and communicating with both the uterine veins and the intervillous space. The pressure in the vessels of the uteroplacental circuit is: in the radial arteries - 80/30 mmHg, in the decidual part of the spiral arteries - 12-16 mmHg, in the intervillous space - about 10 MMHg. Thus, the loss of the muscular-elastic cover by the spiral arteries leads to their insensitivity to adrenergic stimulation, the ability to vasoconstrict, which ensures unimpeded blood supply to the developing fetus. The method of ultrasound Doppler has revealed a sharp decrease in the resistance of the uterine vessels by the 18-20th week of pregnancy, i.e. by the period of completion of the trophoblast invasion. In subsequent periods of pregnancy, the resistance remains at a low level, ensuring high diastolic blood flow.degeneration of the muscular layer and fibrinoid necrosis. Due to this, peripheral vascular resistance and, accordingly, blood pressure decrease. The process of trophoblast invasion ends completely by the 20th week of pregnancy. It is during this period that systemic arterial pressure decreases to its lowest values. Resistance to blood flow from the radial arteries to the intervillous space is practically absent. Blood outflow from the intervillous space is carried out through 72-170 veins located on the surface of the terminal villi and, partly, into the marginal sinus bordering the placenta and communicating with both the veins of the uterus and the intervillous space. The pressure in the vessels of the uteroplacental contour is: in the radial arteries - 80/30 mmHg, in the decidual part of the spiral arteries - 12-16 mmHg, in the intervillous space - about 10 MMHg. Thus, the loss of the muscular-elastic cover by the spiral arteries leads to their insensitivity to adrenergic stimulation, the ability to vasoconstrict, which ensures unimpeded blood supply to the developing fetus. The method of ultrasound Doppler has revealed a sharp decrease in the resistance of the uterine vessels by the 18-20th week of pregnancy, i.e. by the period of completion of the trophoblast invasion. In subsequent periods of pregnancy, the resistance remains at a low level, ensuring high diastolic blood flow.degeneration of the muscular layer and fibrinoid necrosis. Due to this, peripheral vascular resistance and, accordingly, blood pressure decrease. The process of trophoblast invasion ends completely by the 20th week of pregnancy. It is during this period that systemic arterial pressure decreases to its lowest values. Resistance to blood flow from the radial arteries to the intervillous space is practically absent. Blood outflow from the intervillous space is carried out through 72-170 veins located on the surface of the terminal villi and, partly, into the marginal sinus bordering the placenta and communicating with both the veins of the uterus and the intervillous space. The pressure in the vessels of the uteroplacental contour is: in the radial arteries - 80/30 mmHg, in the decidual part of the spiral arteries - 12-16 mmHg, in the intervillous space - about 10 MMHg. Thus, the loss of the muscular-elastic cover by the spiral arteries leads to their insensitivity to adrenergic stimulation, the ability to vasoconstrict, which ensures unimpeded blood supply to the developing fetus. The method of ultrasound Doppler has revealed a sharp decrease in the resistance of the uterine vessels by the 18-20th week of pregnancy, i.e. by the period of completion of the trophoblast invasion. In subsequent periods of pregnancy, the resistance remains at a low level, ensuring high diastolic blood flow.

The proportion of blood flowing to the uterus during pregnancy increases 17-20 times. The volume of blood flowing through the uterus is about 750 ml/min. In the myometrium15% of the blood entering the uterus is distributed, 85% of the blood volume enters directly into the uteroplacental circulation. The volume of the intervillous space is 170-300 ml, and the blood flow rate through it is 140 ml/min per 100 ml of volume. The rate of uteroplacental blood flow is determined by the ratio of the difference between the uterine arterial and venous pressure (i.e. perfusion) to the peripheral vascular resistance of the uterus. Changes in uteroplacental blood flow are caused by a number of factors: the action of hormones, changes in the volume of circulating blood, intravascular pressure, changes in peripheral resistance determined by the development of the intervillous space. Ultimately, these effects are reflected in the peripheral vascular resistance of the uterus. The intervillous space is subject to changes under the influence of changing blood pressure in the vessels of the mother and fetus, pressure in the amniotic fluid and contractile activity of the uterus. During uterine contractions and hypertonicity, due to the increase in uterine venous pressure and intramural pressure in the uterus, the uteroplacental blood flow decreases. It has been established that the constancy of blood flow in the intervillous space is maintained by a multistage chain of regulatory mechanisms. These include the adaptive growth of uteroplacental vessels, the system of organ blood flow autoregulation, coupled placental hemodynamics on the maternal and fetal sides, the presence of a circulatory buffer system in the fetus, including the vascular network of the placenta and umbilical cord, the ductus arteriosus and the pulmonary vascular network of the fetus. Regulation of blood flow on the maternal side is determined by blood movement and uterine contractions, on the fetal side - by rhythmic active pulsation of the chorionic capillaries under the influence of fetal cardiac contractions, the influence of the smooth muscles of the villi and the periodic release of the intervillous spaces. The regulatory mechanisms of uteroplacental circulation include increased contractile activity of the fetus and an increase in its arterial pressure. Fetal development and its oxygenation are largely determined by the adequacy of the functioning of both uteroplacental and fetoplacental circulation.

The umbilical cord is formed from the mesenchymal strand (amniotic pedicle), into which the allantois, carrying the umbilical vessels, grows. When the branches of the umbilical vessels growing from the allantois join with the local circulatory network, circulation of embryonic blood in the tertiary villi is established, which coincides with the onset of the embryo's heartbeat on the 21st day of development. In the early stages of ontogenesis, the umbilical cord contains two arteries and two veins (merge into one at later stages). The umbilical vessels form a spiral of about 20-25 turns due to the fact that the vessels are longer than the umbilical cord. Both arteries are of the same size and supply blood to half of the placenta. The arteries anastomose in the chorionic plate, passing through the chorionic plate into the trunk villus, they give rise to the arterial system of the second and third order, repeating the structure of the cotyledon. Cotyledon arteries are terminal vessels with three orders of division and contain a network of capillaries, the blood from which is collected into the venous system. Due to the excess of the capacity of the capillary network over the capacity of the arterial vessels of the fetal part of the placenta, an additional blood pool is created, forming a buffer system that regulates the blood flow rate, blood pressure, and fetal cardiac activity. This structure of the fetal vascular bed is fully formed already in the first trimester of pregnancy.

The second trimester of pregnancy is characterized by the growth and differentiation of the fetal circulatory bed (fetalization of the placenta), which are closely related to changes in the stroma and trophoblast of the branched chorion. In this period of ontogenesis, the growth of the placenta outpaces the development of the fetus. This is expressed in the convergence of the maternal and fetal blood flows, the improvement and increase in surface structures (syncytiotrophoblast). From the 22nd to the 36th week of pregnancy, the increase in the mass of the placenta and fetus occurs uniformly, and by the 36th week the placenta reaches full functional maturity. At the end of pregnancy, the so-called "aging" of the placenta occurs, accompanied by a decrease in the area of its exchange surface. It is necessary to dwell in more detail on the features of the fetal circulation. After implantation and the establishment of a connection with the maternal tissues, oxygen and nutrients are delivered by the circulatory system. There are sequentially developing circulatory systems in the intrauterine period: yolk, allantoic and placental. The yolk period of development of the circulatory system is very short - from the moment of implantation until the end of the first month of the embryo's life. Nutrients and oxygen contained in the embryotroph penetrate to the embryo directly through the trophoblast, which forms the primary villi. Most of them enter the yolk sac formed by this time, which has foci of hematopoiesis and its own primitive vascular system. From here, nutrients and oxygen enter the embryo through the primary blood vessels.

Allantoid (chorionic) circulation begins at the end of the first month and continues for 8 weeks. Vascularization of the primary villi and their transformation into true chorionic villi mark a new stage in the development of the embryo. Placental circulation is the most developed system, providing for the ever-increasing needs of the fetus, and begins at the 12th week of pregnancy. The embryonic heart rudiment is formed at the 2nd week, and its formation is mainly completed at the 2nd month of pregnancy: it acquires all the features of a four-chambered heart. Along with the formation of the heart, the vascular system of the fetus arises and differentiates: by the end of the 2nd month of pregnancy, the formation of the main vessels is completed, and in the following months, further development of the vascular network occurs. The anatomical features of the cardiovascular system of the fetus are the presence of an oval opening between the right and left atrium and an arterial (Botallo's) duct connecting the pulmonary artery with the aorta. The fetus receives oxygen and nutrients from the mother's blood through the placenta. In accordance with this, the fetal circulation has significant features. Blood enriched with oxygen and nutrients in the placenta enters the body through the umbilical vein. Having penetrated the umbilical ring into the abdominal cavity of the fetus, the umbilical vein approaches the liver, gives off branches to it, and then goes to the inferior vena cava, into which it pours arterial blood. In the inferior vena cava, arterial blood mixes with venous blood coming from the lower half of the body and internal organs of the fetus. The section of the umbilical vein from the umbilical ring to the inferior vena cava is called the venous (Arantius) duct. Blood from the inferior vena cava enters the right atrium, where venous blood from the superior vena cava also flows. Between the confluence of the inferior and superior vena cava is the valve of the inferior vena cava (Eustachian), which prevents the mixing of blood coming from the superior and inferior vena cava. The valve directs the flow of blood from the inferior vena cava from the right atrium to the left through the oval opening located between the two atria; from the left atrium, the blood enters the left ventricle, and from the ventricle, into the aorta. From the ascending aorta, the blood, which contains a relatively large amount of oxygen, enters the vessels supplying blood to the head and upper part of the body. Venous blood that has entered the right atrium from the superior vena cava is directed to the right ventricle, and from it to the pulmonary arteries. From the pulmonary arteries, only a small part of the blood enters the non-functioning lungs; the bulk of the blood from the pulmonary artery enters through the arterial (Botallo's) duct and the descending aorta. In the fetus, unlike in an adult, the right ventricle of the heart is dominant: its ejection is 307+30 ml/min/kg, and that of the left ventricle is 232+25 ml/min/kg. The descending aorta, which contains a significant portion of venous blood, supplies blood to the lower half of the body and the lower limbs. Fetal blood, poor in oxygen,enters the umbilical arteries (branches of the iliac arteries) and through them - to the placenta. In the placenta, the blood receives oxygen and nutrients, is freed from carbon dioxide and metabolic products and returns to the fetus's body through the umbilical vein. Thus, purely arterial blood in the fetus is contained only in the umbilical vein, in the venous duct and branches going to the liver; in the inferior vena cava and ascending aorta, the blood is mixed, but contains more oxygen than the blood in the descending aorta. Due to these features of blood circulation, the liver and the upper part of the body of the fetus are supplied with arterial blood better than the lower. As a result, the liver reaches a larger size, the head and upper part of the body in the first half of pregnancy develop faster than the lower part of the body. It should be emphasized that the fetoplacental system has a number of powerful compensatory mechanisms that ensure the maintenance of fetal gas exchange under conditions of reduced oxygen supply (predominance of anaerobic metabolic processes in the fetal body and in the placenta, large cardiac output and fetal blood flow velocity, the presence of fetal hemoglobin and polycythemia, increased affinity for oxygen in fetal tissues). As the fetus develops, there is some narrowing of the oval opening and a decrease in the valve of the inferior vena cava; in connection with this, arterial blood is more evenly distributed throughout the fetal body and the lag in the development of the lower half of the body is leveled out.

Immediately after birth, the fetus takes its first breath; from this moment, pulmonary respiration begins and the extrauterine type of blood circulation arises. During the first breath, the pulmonary alveoli straighten out and the blood flow to the lungs begins. Blood from the pulmonary artery now flows into the lungs, the arterial duct collapses, and the venous duct also becomes empty. The newborn's blood, enriched with oxygen in the lungs, flows through the pulmonary veins into the left atrium, then into the left ventricle and aorta; the oval opening between the atria closes. Thus, the extrauterine type of blood circulation is established in the newborn.

During fetal growth, systemic arterial pressure and circulating blood volume constantly increase, vascular resistance decreases, and umbilical vein pressure remains relatively low - 10-12 mmHg. Arterial pressure increases from 40/20 mmHg at 20 weeks of pregnancy to 70/45 mmHg at the end of pregnancy. Increase in umbilical blood flow in the first half of pregnancy is achieved mainly due to decreased vascular resistance, and then mainly due to increased fetal arterial pressure. This is confirmed by ultrasound Doppler data: the greatest decrease in fetoplacental vascular resistance occurs at the beginning of the second trimester of pregnancy. The umbilical artery is characterized by progressive blood movement both in the systolic and diastolic phases. From the 14th week, Dopplerograms begin to record the diastolic component of blood flow in these vessels, and from the 16th week it is detected constantly. There is a directly proportional relationship between the intensity of the uterine and umbilical blood flow. Umbilical blood flow is regulated by perfusion pressure determined by the ratio of pressure in the aorta and umbilical vein of the fetus. Umbilical blood flow receives approximately 50-60% of the total cardiac output of the fetus. The magnitude of umbilical blood flow is influenced by physiological processes of the fetus - respiratory movements and motor activity. Rapid changes in umbilical blood flow occur only due to changes in fetal arterial pressure and its cardiac activity. The results of studying the effect of various drugs on uteroplacental and fetoplacental blood flow are noteworthy. The use of various anesthetics, narcotic analgesics, barbiturates, ketamine, halothane can lead to a decrease in blood flow in the mother-placenta-fetus system. In experimental conditions, an increase in uteroplacental blood flow is caused by estrogens, but in clinical conditions, the introduction of estrogens for this purpose is sometimes ineffective. When studying the effect of tocolytics (beta-adrenergic agonists) on uteroplacental blood flow, it was found that beta-mimetics dilate arterioles, reduce diastolic pressure, but cause tachycardia in the fetus, increase blood glucose levels, and are effective only in functional placental insufficiency. The functions of the placenta are varied. It provides nutrition and gas exchange for the fetus, excretes metabolic products, and forms the hormonal and immune status of the fetus. During pregnancy, the placenta replaces the missing functions of the blood-brain barrier, protecting the nerve centers and the entire body of the fetus from the effects of toxic factors. It also has antigenic and immune properties. An important role in performing these functions is played by the amniotic fluid and fetal membranes, which form a single complex with the placenta.

Being an intermediary in the creation of the hormonal complex of the mother-fetus system, the placenta plays the role of an endocrine gland and synthesizes hormones using maternal and fetal precursors. Together with the fetus, the placenta forms a single endocrine system. The hormonal function of the placenta contributes to the preservation and progression of pregnancy, changes in the activity of the endocrine organs of the mother. The processes of synthesis, secretion and transformation of a number of hormones of protein and steroid structure occur in it. There is a relationship between the mother's body, the fetus and the placenta in the production of hormones. Some of them are secreted by the placenta and transported into the blood of the mother and fetus. Others are derivatives of precursors entering the placenta from the mother's or fetus's body. The direct dependence of the synthesis of estrogens in the placenta from androgenic precursors produced in the fetus's body allowed E. Diczfalusy (1962) to formulate the concept of the fetoplacental system. Unmodified hormones can also be transported through the placenta. Already in the preimplantation period at the blastocyst stage, the germ cells secrete progesterone, estradiol and chorionic gonadotropin, which are of great importance for nidation of the fertilized egg. During organogenesis, the hormonal activity of the placenta increases. Of the protein hormones, the fetoplacental system synthesizes chorionic gonadotropin, placental lactogen and prolactin, thyrotropin, corticotropin, somatostatin, melanocyte-stimulating hormone, and of the steroids - estrogens (estriol), cortisol and progesterone.

Amniotic fluid is a biologically active environment surrounding the fetus, intermediate between it and the mother's body and performing various functions throughout pregnancy and labor. Depending on the gestational age, the fluid is formed from various sources. In the embryotrophic ether, the amniotic fluid is a trophoblast transudate, during the period of yolk nutrition - a transudate of the chorionic villi. By the 8th week of pregnancy, the amniotic sac appears, which is filled with fluid similar in composition to the extracellular fluid. Later, the amniotic fluid is an ultrafiltrate of maternal blood plasma. It has been proven that in the second half of pregnancy and until the end of it, the source of amniotic fluid, in addition to the filtrate of maternal blood plasma, is the secretion of the amniotic membrane and umbilical cord, after the 20th week - the product of the fetal kidneys, as well as the secretion of its lung tissue. The volume of amniotic fluid depends on the weight of the fetus and the size of the placenta. Thus, at 8 weeks of pregnancy it is 5-10 ml, and by the 10th week it increases to 30 ml. In the early stages of pregnancy, the amount of amniotic fluid increases by 25 ml/week, and in the period from 16 to 28 weeks - by 50 ml. By 30-37 weeks their volume is 500-1000 ml, reaching a maximum (1-1.5 l) by 38 weeks. By the end of pregnancy, the volume of amniotic fluid can decrease to 600 ml, decreasing every week by about 145 ml. The amount of amniotic fluid less than 600 ml is considered oligohydramnios, and its amount more than 1.5 l - polyhydramnios. At the beginning of pregnancy, amniotic fluid is a colorless transparent liquid, which changes its appearance and properties during pregnancy, becomes cloudy, opalescent due to the secretion of the sebaceous glands of the fetus's skin, vellus hairs, epidermal scales, amnion epithelial products, including fat droplets. The quantity and quality of suspended particles in the waters depend on the gestational age of the fetus. The biochemical composition of amniotic fluid is relatively constant. There are minor fluctuations in the concentration of mineral and organic components depending on the gestational age and the condition of the fetus. Amniotic fluid has a slightly alkaline or close to neutral reaction. Amniotic fluid contains proteins, fats, lipids, carbohydrates, potassium, sodium, calcium, trace elements, urea, uric acid, hormones (human chorionic gonadotropin, placental lactogen, estriol, progesterone, corticosteroids), enzymes (thermostable alkaline phosphatase, oxytocinase, lactate and succinate dehydrogenase), biologically active substances (catecholamines, histamine, serotonin), factors affecting the blood coagulation system (thromboplastin, fibrinolysin), and fetal blood group antigens. Consequently, amniotic fluid is a very complex environment in terms of composition and function. In the early stages of fetal development, amniotic fluid is involved in its nutrition, promotes the development of the respiratory and digestive tracts.Later they perform the functions of the kidneys and skin. The rate of exchange of amniotic fluid is of the utmost importance. Based on radioisotope studies, it has been established that during a full-term pregnancy, about 500-600 ml of water is exchanged within 1 hour, i.e. 1/3 of it. Their complete exchange occurs within 3 hours, and the complete exchange of all dissolved substances - within 5 days. Placental and paraplacental pathways of amniotic fluid exchange (simple diffusion and osmosis) have been established. Thus, the high rate of formation and reabsorption of amniotic fluid, the gradual and constant change in its quantity and quality depending on the gestational age, the condition of the fetus and mother indicate that this environment plays a very important role in the metabolism between the organisms of the mother and fetus. Amniotic fluid is the most important part of the protective system that protects the fetus from mechanical, chemical and infectious effects. They protect the embryo and fetus from direct contact with the inner surface of the fetal sac. Due to the presence of a sufficient amount of amniotic fluid, fetal movements are free. Thus, a deep analysis of the formation, development and functioning of the unified mother-placenta-fetus system allows us to reconsider some aspects of the pathogenesis of obstetric pathology from a modern perspective and, thus, develop new approaches to its diagnostics and treatment tactics.

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