What membrane surrounds the fetal egg. The membranes and amniotic fluid. Symptoms and signs of detachment of the fetal egg

The discovery of a fetal egg in the uterine cavity means the onset of pregnancy. A woman can accept congratulations. However, in practice, joy is almost immediately replaced by anxieties - is everything in order with the baby, does the fetal egg meet the standards? We will talk about how the fetal egg is arranged and what its dimensions should be during normal development in this article.

Appearance and structure

The amnion is the inner lining of the fetal sac. It produces amniotic fluid - a special nutrient medium in which the embryo and other embryonic structures are located. Chorion is the outer shell. It contains villi, with which the fetal egg is attached to the endometrium of the uterus.

The yolk sac is a "food storehouse" that contains nutrients. It looks like a small yellowish pea located between the chorion and amnion at the site of the umbilical cord.

It seems possible to consider the fetal egg only from the 5th week of pregnancy, when its size becomes sufficient for visualization on ultrasound. In other words, you can see it only after a week or more from the moment the next menstruation is delayed.

The color of the membranes is grayish, the shape is oval or rounded. Since the shells are quite elastic, under the influence of various factors (for example, the tone of the uterus), the fetal egg can change shape, but when these factors are eliminated, it quickly returns to its original appearance. The embryo looks like a small strip in it.

The presence of one fetal egg does not guarantee that one child will be born. In the case of monozygotic twins, the embryos develop in one fetal egg. If two fetal eggs are found, this means that the woman is not expecting twins who are similar to each other and have the same sex, but twins, each of which will have a separate “house” during fetal development - a fetal egg, a placenta.

Usually, a fetal egg during pregnancy is determined in the upper third of the uterine cavity. If it is located low, this can significantly complicate the course of pregnancy, since it is dangerous with a complete or partial placenta previa, which is formed at the site of attachment of the chorionic villi to the endometrium of the uterus. The process itself is called implantation or nidation and occurs about a week after fertilization.

Weekly sizes

The size of the fetal egg in the early stages of pregnancy is the main parameter by which the doctor can judge how the baby develops. The embryo is still very small, it is not possible to measure it and its individual parts, but the growth rate of the fetal egg is a very informative indicator of the development of pregnancy as a whole.

The size of the fetal egg speaks not only of development, but also of compliance with certain obstetric terms. The fact is that at the very beginning of pregnancy, when the embryo is just emerging, there is not much difference in height and weight. It is much later that children in the mother's womb begin to grow differently, in accordance with their genetic program (some are tall, others are small). In the meantime, all babies develop almost identically, so the growth rate of the fetal egg is almost the same.

The errors and range of values ​​in the diagnostic tables are associated with the likelihood of late implantation, as well as with other factors that may affect the size of the fetal egg, but do not pose a threat to the development of the baby.

A special technique is used for the measurement. The ultrasound diagnostician draws a straight visual line through the fetal egg, which he sees on the monitor, so that the ends of the segment are located at opposite points of the inner membrane of the fetal sac. This size is called SVD - the average inner diameter.

This size is determined very first. Then the coccyx-parietal size of the embryo itself is added to it. The size of the yolk sac is also important.

Too bad if it doesn't render at all. If it is visible and its dimensions correspond to the norms, this still does not guarantee that the baby will be healthy, that the pregnancy will proceed without problems.

Growth rates can be seen in the table.

Correspondence table for the size of the fetal egg.

Thus, it is considered completely normal if at 5 obstetric weeks - a week after the start of the delay, a woman will find a fetal egg, the size of which will be 4-5 mm. And at 7 obstetric weeks, a fetal egg measuring 20 mm in size will be completely normal. The detection of discrepancies in size with the terms may indicate certain pathologies. But a lag should be understood as a significant deviation, for example, with a gestational age of 7 weeks, the size of the fetal sac is 4-5 mm. Let's look at what are the pathologies of the fetal egg and what is the prognosis.

Pathologies

When the doctor says that the fetal egg is located, but it is elongated, deformed, you should not panic. In most cases, this is due to the increased tone of the uterine muscles; when this phenomenon is eliminated, the fetal membranes will take on completely normal forms. Medicine has a lot of ways to relieve increased tone and prevent miscarriage in the early stages. Among other problems that may be detected during the passage of an ultrasound examination, the following can be noted.

hypoplasia

This is an anomaly in which the development of the fetal membranes lags behind the growth rate of the embryo itself. The fertilized egg, therefore, differs from the embryo in size and timing. According to the diameter of the fetal sac, the doctor puts only 7 weeks, and according to the size of the embryo - 9 weeks.

The reasons why hypoplasia occurs are multifaceted. This can be taking antibiotics in the early stages, influenza or ARVI transferred at the initial stages of pregnancy, hormonal disorders in the woman's body (endocrine diseases, hormonal stimulation as part of the IVF protocol), as well as fetal malformations. The prognosis, alas, is unfavorable. In most cases, the embryo becomes too crowded in small shells and it dies. There is a frozen pregnancy.

A fetal egg that does not grow or grows too slowly gives an inadequate increase in the blood of the pregnancy hormone hCG, because the chorionic villi do not cope with their duties, including the production of this substance necessary for bearing the fetus.

bubble skid

A gross and total anomaly in which the embryo does not develop, but the chorionic villi grow and turn into a mass of small bubbles resembling bunches of grapes. With a complete drift, the embryo is completely absent; with an incomplete one, the embryo and other structures of the fetal egg may be present, but cannot develop normally.

The reasons for this phenomenon are as a female reproductive cell. If a spermatozoon fertilizes an oocyte devoid of DNA, just such a pathology develops. Only the paternal chromosomes are doubled; such an embryo is not viable in principle. If one egg is fertilized by two spermatozoa at once (which happens, although rarely), an incomplete mole will be formed.

At the same time, hCG will “go off scale”, because the overgrown chorionic villi will produce it in excess, which can cause the development of cysts in the female sex glands. But it is dangerous not only for this - in 17-20% of cases, the skid turns into chorionepithelioma. This is a malignant tumor that causes cancer and quickly gives multiple metastases.

If a cystic drift is detected, the uterine cavity is cleaned of formation, vacuum aspiration (essentially an abortion) or curettage (curettage of the uterine cavity) is performed.

Anembryony

This is a pathology in which there is a fetal egg, it grows, but the embryo inside it is completely absent. The anomaly is also called the empty gestational sac syndrome. This is detected on ultrasound after 6-7 weeks of pregnancy, when the doctor fails to hear the baby's heartbeat and see the fetus.

Up to 80% of anembryonic cases are the consequences of gross genetic pathologies during conception. Also, the reasons may lie in the flu and other acute viral illnesses suffered by a woman. Anembryonia can be the result of an untreated bacterial infection of the genital tract, as well as endometriosis.

More often, pathology occurs in women living in regions with unfavorable radiation conditions. Also, pathology is often found in women with metabolic disorders (especially with deficiency and impaired production of progesterone).

If anembryony is suspected, a woman is prescribed several control ultrasounds with a difference of several days. If suspicions are confirmed, the embryo is still not visible, curettage or vacuum aspiration is performed.

False fertilized egg

This situation is one of the most difficult to diagnose. A fetal egg is found in the uterus, but it categorically does not correspond to the deadline, there is a significant growth lag. Also, it is not possible to detect an embryo in it, as is the case with the syndrome of an empty ovum. However, the deceit lies not in this, but in the fact that outside the uterus, with a high degree of probability, a second fetal egg develops, that is, an ectopic pregnancy occurs.

Low location

If the fetal egg is found not in the upper third of the uterus, but below, this requires careful medical supervision. But it's too early to draw conclusions. The uterus in the process of growth during pregnancy increases, and the fetal egg can "migrate" higher. If it develops normally, according to the gestational age, then nothing but observation is required in this situation.

amniotic septum

This pathology occurs in approximately one case per one and a half thousand pregnancies. The amnion forms strands - a septum is formed inside the fetal egg. This, of course, requires careful monitoring by doctors.

The reasons for the development of the anomaly are not fully understood, but doctors tend to believe that the strands are formed due to damage to the fetal egg at the earliest stages of development. It is quite possible to endure and give birth to a child with a septum inside the membranes, but the birth of a child with clefts (“cleft palate”, “hare lip”) is not excluded. The limbs of the baby may also suffer due to prolonged squeezing. Sometimes it leads to necrosis of the limbs and their subsequent amputation after the birth of a child.

Quite often, children born after intrauterine stay in a bladder with a septum suffer from valgus deformity of the feet. The frequency of such negative outcomes is 12-15%. The rest of the women bear a child without terrible consequences for his health.

In addition, it is not at all necessary that the septum will remain throughout the pregnancy. If it was found on one ultrasound, then on the next it may no longer be, because the septum is so thin that it may well break.

Large fertilized egg

Too large a fetal egg in the early stages can indicate various pathologies of both the fetus itself and this pregnancy. Often, excess size is a harbinger of a missed pregnancy, quite often it is combined with fetal heart rhythm disturbances, with the embryo itself lagging behind in standard sizes.

A slight increase in the fetal egg for a period of 5-6 weeks may indicate that one egg is visualized, but it may well contain two embryos (monochorial twins, twins). Usually in this case, a blood test for hCG is done and an ultrasound is repeated a week later to examine both embryos.

Retrochorial hematoma

Due to the partial detachment of the chorion from the uterine wall, a hematoma may develop - blood accumulates between the chorion and the endometrium. This pathology is usually manifested by the appearance of bloody discharge from the genitals, as well as weak pulling pains in the lower abdomen.

The prognosis depends on the size of the hematoma. If discharge appears, this is a favorable sign, which indicates that it is decreasing, blood is coming out. In the future, the pregnancy will proceed completely normally.

If the hematoma grows, but there is no discharge or they are very abundant, it is likely that a complete detachment of the fetal egg will occur (or has already occurred). It is not possible to save a pregnancy in such a situation.

In most cases, retrochorial hematoma develops in women who are a lot of nervous, are in a state of constant stress, in women with hormonal imbalances, with endometriosis and other pathologies of the reproductive system. Excessive physical exertion, and unreasonably taken medications, for which the attending physician did not give permission, can also become the cause of detachment.

What to do when anomalies are detected?

First of all, a woman needs to calm down and trust her doctor. If the fetal egg shows too little growth now, it is possible that in a week or two it will fully comply with the norms. Therefore, a woman is assigned several ultrasound examinations. Any pathology, if it takes place, requires multiple confirmation.

The fertilized egg is so small and elastic that an inexperienced doctor may well see something in it that is not really there, or vice versa. Therefore, it is quite acceptable for a woman to turn to another specialist for a second study, quite often it does not confirm the disappointing and alarming results of the first ultrasound.

When the fetal egg is deformed, if the embryo is of normal size, its heartbeat is well heard, the woman is prescribed moral and physical rest, taking vitamins, as well as drugs that reduce the tone of the smooth muscles of the uterus - No-Shpy, Papaverine, magnesium and iron preparations .

If gross pathologies are detected - hydatidiform mole, anembryony, etc., it is not possible to maintain the pregnancy. A woman should know that she can still have children, the main thing is to find the cause of the development of the anomaly in this case. This will help in planning future pregnancies. Be sure to check with your doctor if a genetic study of the aborted mass, fetal membranes will be carried out. If genetic disorders are established, be sure to visit a geneticist before planning the next pregnancy.

For information on how the conception and development of the fetal egg occur, see the following video.

FERTILIZATION AND DEVELOPMENT OF THE FETAL EGG. CRITICAL PERIODS OF DEVELOPMENT. PLACENTA

FERTILIZATION AND DEVELOPMENT OF THE EGG

Fertilization is the process of fusion of male (sperm, sperm) and female (ovum) germ cells containing a haploid (single) set of chromosomes, as a result of which a diploid set of chromosomes is restored and a qualitatively new cell is formed - a zygote, which gives rise to a new organism.

Fertilization of the eggs of mammals (including humans) occurs in the ampulla of the fallopian tube, where only a small amount of sperm reaches. The duration of time during which ovulated eggs are able to be fertilized usually does not exceed 24 hours. Spermatozoa lose their fertilizing ability, being in the female genital tract for about the same time, therefore, for fertilization, they need to meet in a certain and short period of time.

Spermatozoa isolated from the tubules of the testis, where they are formed, are practically immobile and incapable of fertilization. They acquire fertilizing ability, being within a few days in the tubules of the epididymis (epididymis), moving passively from its caudal part to the cranial. At this time, the spermatozoa "ripen", acquire the ability to active movements.

During sexual intercourse, the ejaculate enters the woman's vagina, under the influence of the acidic environment of which part of the spermatozoa dies, and part penetrates through the cervical canal into the lumen of the uterus, where there is an alkaline environment that helps maintain their mobility. When spermatozoa come into contact with the cells of the fallopian tube and uterus, they undergo a process called capacitation.

Capacitation is currently understood as the acquisition by spermatozoa of the ability to penetrate through the membranes into the egg.

The egg after ovulation, in addition to the zona pellucida, is surrounded by several layers of cells of the oviparous tubercle (Fig. 15). To overcome this barrier, the spermatozoon has a special organelle, the acrosome, which is a membranous vesicle located at the top of its head (Fig. 1b). The acrosomal reaction is induced by the contact of the spermatozoon with the cells of the oviparous tubercle. Its morphological expression is the fusion of the acrosomal and plasma membranes of the spermatozoon. This releases the contents of the acrosome, which includes 10-12 different enzymes that facilitate the passage of spermatozoa through the membranes surrounding the egg. After passing through the zona pellucida, the sperm enters the perivitelline space, after which the fusion of gametes takes place, which takes several minutes.

It takes one sperm to fertilize a human egg. When “extra” spermatozoa penetrate the egg, the normal course of development is disrupted, and the embryo inevitably dies.

Normally, after penetration into the egg of one sperm, a “barrier” arises against the penetration of others. The most important role in its formation belongs to the cortical reaction, during which the contents of the cortical granules, which were previously located under the plasma membrane of the egg, are released from the egg. The content of the cortical granules attaches to the material of the egg cell membrane, changing its properties, as a result of which it becomes impermeable to other sperm. In addition, there is its separation from the surface of the egg and a significant increase in the perivitelline space. Probably, the characteristics of the plasma membrane of the egg also change. An additional factor that reduces the likelihood of penetration of several sperm into the egg is a small number of them, penetrating into the place of the fallopian tube where fertilization occurs.

After the penetration of the sperm into the egg, its chromosomes, which are part of the metaphase II of meiosis, diverge into two groups, one of which is part of the polar body, and the second subsequently forms the female pronucleus. After the completion of the second meiotic division, the maternal set of chromosomes is converted into a nucleus called the female pronucdeus, and the sperm head is converted into a nucleus called the male pronucleus. During the formation of the male pronucleus, the membrane of the sperm nucleus is destroyed, the chromatin swells and decondenses, and then a new nuclear envelope forms around it. Subsequently, the parental sets of chromosomes are combined into a single cell nucleus system and the zygote enters cleavage, during which it is divided into blastomeres.

In the early stages of development, the blastomeres are pluripotent, and the embryos have a high regulatory capacity: each of the first two or four blastomeres, if isolated, is capable of developing into a full-fledged embryo. After the third division, processes are carried out that predetermine the ways of blastomere differentiation. As a result of subsequent divisions of crushing, a morula is formed (Fig. 17, a), which is a spherical accumulation of blastomeres.

The next stage (blastocyst) is characterized by the formation of a cavity filled with fluid secreted by blastomeres (Fig. 17.6). When the morula is transformed into a blastocyst, the blastomeres are reorganized, and they are divided into two subpopulations - external and internal. The inner cells form the inner cell mass (embryoblast), from which the germinal nodule, extraembryonic mesenchyme, amnion and yolk sac subsequently develop, and the outer cells form the trophoblast necessary for implantation (see Fig. 17).

During the crushing period, the embryo moves along the fallopian tube to the uterus. Migration lasts 6-7 days, after which the embryo enters the uterine cavity and is introduced into the mucous membrane of its wall. This process is called implantation. Before implantation begins, the blastocyst emerges from the zona pellucida, which is associated both with the mechanical effects of the pulsation of the blastocyst itself and with the fact that the uterus produces a number of factors that cause lysis of this membrane. After leaving the zona pellucida, the blastocyst orients itself in the uterine crypt, which is important both for the implantation process and for the further development of the embryo.

During implantation, there is a change in the physical and biochemical properties of the surface of the trophecgodermis and the epithelium of the uterus. During the adhesion phase, microvilli of endometrial cells disappear;

By the time of implantation, the uterine mucosa is in the secretion phase: the epithelium of the glands begins to secrete a secret containing glycogen and mucin, the lumen of the glands expands, the stroma cells of the surface part of the functional layer are transformed into decidual cells that are large and contain a large nucleus. After attaching the blastocyst to the wall of the uterus, the integumentary epithelium of the uterine mucosa is destroyed by the action of the trophoblast, and the embryo gradually sinks deep into the functional layer of the endometrium. The process of encapsulation of the embryo ends with the restoration of the mucous membrane over the site of its introduction. After implantation, the functional layer of the mucous membrane thickens, and the glands in it become even more filled with secretions. Stroma cells increase, the amount of glycogen in them increases. These cells are called decidual cells of pregnancy.

In the process of implantation, the trophoblast grows and forms a chorion from it, giving processes (villi) deep into the functional layer of the endometrium of the uterus, destroying the surface network of endometrial capillaries, which leads to the outpouring of blood and 1 formation of lacunae. The strands of trophoblast separating the lacunae are called cervical villi. With their appearance, the blastocyst is called the fetal bladder. Extra-embryonic mesenchyme grows in the cavity of the blastocyst (fetal bladder). The extra-embryonic mesenchyme lining the trophoblast forms together with it the chorionic plate. The ingrowth of connective tissue (mesoderm) into the primary villi leads to their transformation into secondary ones. The connective tissue basis of such villi is their stroma, and the trophoblast is the epithelial cover. In early pregnancy, the trophoblastic epithelium is represented by two layers. The cells of the inner layer consist of spherical Langhans cells and are called cytotrophoblasts. The cells of the outer layer are syncytium, which does not have cellular elements, representing a layer of cytoplasm with a large number of nuclei. In the early stages of pregnancy, syncytium forms cytoplasmic outgrowths, later - kidneys, and in the third trimester of pregnancy - synpitial nodes (areas of thickening of the cytoplasm with accumulation of nuclei). Implantation is completed by the 12-13th day of pregnancy.

The embryoblast develops simultaneously with the trophoblast. In parallel with the implantation process, troblastic and entoblastic vesicles surrounded by mesoblasts form from embryoblast cells. Later, amniotic fluid and its wall, the amniotic membrane (amnion), is formed from the ectoblastic vesicle. The entoblastic vesicle becomes the vitelline cavity. From the cells of the ectoblast, mesoblast and entoblast, 3 germ layers (ectoderm, mesoderm and endoderm) are formed, from which all tissues and organs of the fetus are formed. As the amniotic cavity enlarges, the yolk sac undergoes atrophy. From the posterior end of the primary intestine of the embryo, you form an outgrowth - the allantois, along which vessels subsequently go from the body of the embryo to the chorion villi.

After implantation is completed, a decidua is formed around the embryo, which is a functional layer of the uterine mucosa modified due to pregnancy. The decidua can be divided into the following sections (Fig. 18), decidua basalis is the area between the embryo and myometrium, decidua capsularis is the area of ​​the shell covering the embryo from above, and decidua parietalis is the rest of the shell. In the course of further development from d. basalis forms the maternal part of the placenta.

Placentation begins from the 3rd week of pregnancy. It is characterized by the development of a vascular network of villi with the transformation of secondary (avascular) villi into tertiary ones. The vascular network is formed from local rudiments (angioblasts) and umbilical vessels of the embryo, growing from the allantois. Large branches of the umbilical vessels (arteries and veins) penetrate the chorionic plate and the villi extending from it. As the villi branch, the diameter of the vessels decreases, and in the terminal villi they are represented only by capillaries. When the network of umbilical vessels is connected to the local vascular network, fetal-placental blood flow is established. The syncytium of the villus is washed by maternal blood, which is poured into the intervillous space when the spiral arteries of the endometrium are opened (beginning of the 6th week of pregnancy). By the end of the 8th week of pregnancy, part of the villi that has penetrated the decidua capsularis stops growing and gradually atrophies. Their other part, which penetrated the decidua basalis, forms the fetal part of the placenta. With the establishment of fetal-placental blood flow, by the end of the 13th week of pregnancy, the period of placentation ends. By this date, i.e. by the end of the first trimester, the main structures of the placenta are formed. Such structural components are: the chorionic plate, together with the adjacent fibrinoid (Langhans band), the villous chorion, the intervillous space, and the basal plate, consisting of the depidual maternal tissue, cytotrophoblast, and the zone of necrosis, or the Nitabuch band.

The fetal egg consists of the fetus, its membranes and amniotic fluid.

The aqueous membrane - the amnion - is the inner membrane of the fetal sac, directly washed by the amniotic fluid, which is also produced by it. It consists of a thin, avascular, transparent membrane, in which two layers are distinguished: the inner (epithelial), facing the fetus, and the outer (connective tissue), closely adjacent to the chorion.

The single-layer low cylindrical epithelium of the amnion gives its fruit surface a shiny smooth appearance. The connective tissue layer lined by it consists of embryonic tissue. The amnion, with its connective tissue layer, is fused with the fruiting surface of the chorion throughout its entire length up to the place of attachment of the umbilical cord to the placenta. However, this fusion is only apparent, since it is usually easy to separate a transparent translucent thin amnion from a denser, somewhat rough and less transparent chorion.

The villous membrane, chorion, is the second membrane of the fetal egg. The chorion is divided into two sections: the branched chorion (chorion frondosum), consisting of lushly developed villi, and the smooth chorion (chorion leve), completely devoid of villi. At the same time, the smooth chorion is the second layer of that part of the fetal sac, which is actually called the membranes of the fetus, while the branched chorion goes to build the placenta.

The falling off shell, decidua, is the maternal tissue. It intimately adjoins the chorion along its entire outer surface. By the end of pregnancy, it sharply becomes thinner, the surface layer of the epithelium covering it disappears, and the epithelium of the glands embedded in it flattens and takes on the appearance of an endothelium.

The placenta is formed from a branched chorion. It looks like a thick flatbread with a diameter of about 18 cm, a thickness of 3 cm and a weight of 500-600 g.

There are two surfaces on the placenta: fetal and maternal.

The fruit surface is covered with amnion. Through the amnion, a well-developed network of vessels overflowing with blood - arteries and veins, radially diverging from the place of attachment of the umbilical cord to the periphery, clearly emerges. By the nature of the structure, they are more often loose, less often the main type. The caliber of the vessels gradually decreases as they approach the edge of the placenta.

The maternal surface of the born placenta is covered with a matte thin grayish coating, the remnant of the falling off membrane. Under the latter, 15-20 lobules are quite clearly visible. The connective tissue of the falling off membrane penetrates between the individual lobules and forms partitions between them.

The vascular network of the placenta consists of two systems: uteroplacental and fetal.

The uteroplacental arteries bring blood from the vessels of the uterus to the intervillous spaces of the falling membrane, from where the blood flows back to the uterus through the uteroplacental veins.

The fetal vessels consist of branches of two umbilical arteries. Each lobule usually has one arterial branch (a branch of the second order), which, upon entering the lobule, breaks up into branches of the third order. The number of the latter corresponds to the number of villi. Branches of the third order break up into capillaries, the ends of which pass into venous capillaries, merging further into ever larger vessels and, finally, passing into the umbilical vein. Thus, each lobule of the placenta consists of a rich vascular network.

The umbilical cord (funiculus umbilicalis) is an elongated, shiny, smooth, whitish, usually spirally twisted, dense rod that connects the fetus to the child's place. The length of the umbilical cord is 50-60 cm, the diameter is 1-1.5 cm. One end of the umbilical cord is attached to the fetus in the umbilical ring, and the other end to the placenta. Attachment of the umbilical cord to the latter can be central, eccentric, marginal or sheath.

On the section of the umbilical cord, three vessels are visible: one vein (with a wide lumen, thin-walled) and two arteries. Outside, the umbilical cord is covered with an amnion, which, not reaching the navel by 1–0.5 cm, passes into the skin of the fetus. The placenta with the umbilical cord and membranes is called the placenta.

Amniotic fluid, or amniotic fluid, is clear in the first half of pregnancy. In the second half of pregnancy, especially towards the end of it, they become somewhat cloudy. This turbidity depends on the formed elements mixed with the fetal waters: delicate hairs (lanugo) of the skin of the fetus, cells of its epidermis, as well as fatty lumps (vernix caseosa) that cover the skin of the fetus in the form of a curdled mass and protect it from maceration. Amniotic fluid is a product of secretory activities of the amnion epithelium.

Fetus. Its length is 49-50 cm, weight 3200-3500 g. The skin is pale pink, smooth, the fluff is preserved only in the area of ​​the shoulder girdle. Nails protrude beyond the edges of the fingers. The length of the head is a quarter of the entire length of the fetus. Signs of fetal maturity are: sufficient development of subcutaneous fat, pink skin; the fluff is preserved only on the shoulder girdle, on the upper parts of the back and on the shoulders; hair on the head not less than 2 - 3 cm long; the cartilages of the auricles and nose are dense; the nails are hard and on the fingers go beyond the tips of the latter; the place of discharge of the umbilical cord is located in the middle between the womb and the xiphoid process or slightly lower; in boys, the testicles (with a few pathological exceptions) descended into the scrotum; in girls, the clitoris and labia minora are covered by the labia majora.

The mature fetus is very active: it moves its limbs, makes a loud cry.

3) Changes in the respiratory and digestive systems during pregnancy.

Significant changes that have a pronounced adaptive character occur during pregnancy and respiratory. Along with the circulatory system, the respiratory organs provide a continuous supply of oxygen to the fetus, which increases by more than 30-40% during pregnancy.

With an increase in the size of the uterus, the abdominal organs gradually shift, the vertical size of the chest decreases, which, however, is compensated by an increase in its circumference and an increase in diaphragm excursion. However, the restriction of diaphragmatic excursion during pregnancy makes it somewhat difficult to ventilate the lungs. This is expressed in a slight increase in breathing (by 10%) and in a gradual increase in the respiratory volume of the lungs by the end of pregnancy (by 30-40%). As a result, the minute volume of breathing increases from 8 l / min at the beginning of pregnancy to 11 l / min at the end of it.

Increased tidal volume occurs due to a decrease in the reserve volume, while the vital capacity of the lungs remains unchanged and even slightly increases. During pregnancy, the work of the respiratory muscles increases, although airway resistance decreases towards the end of pregnancy. All these changes in the function of respiration ensure the creation of optimal conditions for gas exchange between the organisms of the mother and fetus.

Many women in the early stages of pregnancy experience nausea, vomiting in the morning, taste sensations change, and intolerance to certain foods appears. As the gestational age increases, these phenomena gradually disappear.

Pregnancy renders inhibitory effect on the secretion of gastric juice and its acidity. All sections of the gastrointestinal tract are in a state of hypotension due to changes in topographic and anatomical relations in the abdominal cavity due to an increase in the pregnant uterus, as well as neurohormonal changes inherent in pregnancy. Here, the effect of placental progesterone on the smooth muscles of the stomach and intestines is of particular importance. This explains the frequent complaints of pregnant women about constipation.

Significant changes in liver function. There is a significant decrease in glycogen stores in this organ, which depends on the intensive transition of glucose from the mother's body to the fetus. The intensification of glycolysis processes is not accompanied by hyperglycemia, therefore, in healthy pregnant women, the nature of glycemic curves does not change significantly. The intensity of lipid metabolism changes. This is expressed by the development of lipemia, a higher content of cholesterol in the blood. The content of cholesterol esters in the blood also increases significantly, which indicates an increase in the synthetic function of the liver.

At physiological course of pregnancy protein formation also changes liver function, which is aimed primarily at providing the growing fetus with the necessary amount of amino acids, from which it synthesizes its own proteins. At the beginning of pregnancy, the content of total protein in the blood of pregnant women is within the normal values ​​characteristic of non-pregnant women. However, starting from the second half of pregnancy, the concentration of total protein in the blood plasma begins to decrease slightly. Pronounced shifts are also observed in the protein fractions of the blood (a decrease in the concentration of albumin and an increase in the level of globulins). This, apparently, is due to the increased release of finely dispersed albumins through the capillary walls into the mother's tissues, as well as their increased consumption by the growing body of the fetus.

An important indicator of liver function in pregnant women is the enzymatic spectrum of blood serum. It has been established that in the course of physiological pregnancy there is an increase in the activity of aspartate-minotransferase (ACT), alkaline phosphatase (AP), especially its thermostable fraction. Other liver enzymes undergo somewhat smaller changes.

During pregnancy in the liver the processes of inactivation of estrogens and other steroid hormones produced by the placenta are enhanced. Detoxification function of the liver during pregnancy is somewhat reduced. Pigment metabolism during pregnancy does not change significantly. Only at the end of pregnancy, the content of bilirubin in the blood serum increases slightly, which indicates an increase in the process of hemolysis in the body of pregnant women.

The placenta is an organ that communicates the fetus with the mother's body, which is torn out of the uterine cavity after the birth of the fetus. The placenta consists of (see), fetal membranes and (see). The fetal membranes form a fetal sac, extend from the edge of the placenta and can easily be divided into their constituent leaves - chorion (hairy membrane), amnion (aqueous membrane) and part of the decidual membrane (see) adjacent to the fetal egg.

Chorion- the outer shell of the fetal egg (); covered with villi that grow into the mucous membrane of the uterus, participating in the formation of the placenta. The chorion begins to function in the early stages of embryogenesis, performing trophic, respiratory, excretory, and protective functions. Chorion, developing from the trophoblast and mesoblast, forms the outer membrane of the fetal sac. At the beginning of development, it is covered with avascular villi. At the end of the first month of pregnancy, vessels from allantois grow into them. In the second month of pregnancy, atrophy of the chorionic villi begins, facing the uterine cavity. On the other part of the chorion, which faces the wall of the uterus, the villi grow, branch, forming the fetal part of the placenta. Each villus consists of a central rod formed by connective tissue with capillaries passing through it. Outside, the villus is covered, consisting of two layers: syncytium and Langhats cells. The epithelial cover of the villi has the ability to melt the underlying uterine mucosa, due to which the nidation (introduction into the endometrium) of the fertilized egg is carried out, and further delivery of nutrients to the fetus.

The placenta is an organ of communication between the fetus and the mother's body, which is rejected from the uterine cavity after the birth of the fetus. Among obstetricians and anatomists, until recently, there is no consensus about which parts of the fetal egg are part of the placenta. It is wrong to identify the concept of the placenta with the placenta, which, although it is part of it, is an independent organ with a complex intrasecretory function.

Some authors understand the afterbirth (secundinae) as the placenta, or baby's place, fleecy and water membranes and the umbilical cord. Other authors, in addition to the fetal membranes (the membranes in which the fetus is located along with the umbilical cord and waters), refer to the placenta and part of the falling off membrane presenting to the fetal egg (decidua basalis), but do not include the umbilical cord. If by the afterbirth we understand everything that comes out of the uterus after the birth of the fetus, then the placenta (see), egg membranes, part of the falling membrane and the umbilical cord should be included in the afterbirth.

Falling off shell reaches its maximum power at the 3-4th month of pregnancy. In the future, it gradually becomes thinner as a result of the melting action of the villi that penetrate into it. Its compact layer with vessels disappears; in the deep spongy layer, which is in contact with the villi that corrode the walls of an extensive network of capillaries, intervillous spaces are formed into which the chorionic villi are immersed. By the end of pregnancy, the falling off membrane turns into a thin plate with the remnants of the glandular layer, adjacent to the muscular layer of the uterus. The remaining sections of the membrane in places where the vessels pass give septa (septa placenthae), penetrating into the thickness of the fruiting part of the placenta, dividing it into separate lobules. The decidua (see) is the maternal part of the placenta. The entire uterine surface of the placenta is covered with a thin, grayish-white film, which is the tissue of the falling membrane.

The aqueous membrane, or amnion, develops very early from the walls of the amniotic sac. The amnion grows rapidly, the amniotic cavity fills most of the cavity of the blastocyst, and then the amniotic sac. The fetal bladder is a part of the membranes of the fetus, located in front of the presenting part, filled with anterior waters. The amniotic sac presses the atrophying yolk sac against the chorion, while dressing the emerging umbilical cord from the outside. By the end of pregnancy, the aqueous membrane, covered with a cylindrical and cubic epithelium, fuses with a smooth chorion (chorion leve), from which it can be separated, with the exception of the area that passes to the umbilical cord. It is customary to consider the water shell as an avascular formation. However, in the early stages of pregnancy, a dense network of lymphatic capillaries and capillary-type blood vessels was found in the amnion wall, located under the epithelium in the connective tissue base of the amnion.

fleecy shell, or chorion, is formed as a result of the fusion of the trophoblast with the mesoderm of the allantois. Already on the 2nd month. pregnancy, it is covered with villi on all sides. At the 3rd month the part of the chorion adjacent to the twisted membrane loses the villi, turning into a smooth chorion (chorion leve). The villi on the part adjacent to the decidua grow strongly and form the fruiting part of the placenta. Each villus consists of a central rod (of fibrous connective tissue) and a capillary vessel. Outside, the rod is covered with an epithelial cover, consisting of two layers - syncytium and Langhans cells. The epithelial cover of the villi has the ability to melt the uterine mucosa during egg implantation, and later - the tissue of the falling membrane, opening the lumen of its blood vessels. This process is of great physiological importance throughout pregnancy (see): through the cells of the epithelial cover of the villi, nutritious material for the fetus is borrowed from maternal blood. The enzymatic activity of the epithelium of the villi is also important.

Natural conception occurs as a result of sexual intercourse between a man and a woman. Currently, methods of artificial insemination and even fertilization outside the body of a woman have been developed, but this is carried out only in case of pathology.

Fertilization is the process of fusion of male and female sex cells. This process takes place in the ampulla of the fallopian tube. Each of the sex cells, or gametes, has 23 chromosomes. After their fusion, a zygote with 46 chromosomes is formed.

Embryogenesis. The zygote is divided into blastomeres, first into 2, then into 4, and so on, until, as a result of crushing, a morula is formed, which is a spherical accumulation of blastomeres. The morula develops into a blastocyst. Its surface turns into a trophoblast, and an embryoblast is formed inside.

An ectoblastic nodule forms in the blastocyst, then it turns into a vesicle, from which the amniotic cavity subsequently forms. From the entoblastic nodule - the entoblastic vesicle, which then turns into the yolk sac. Between the amniotic cavity and the yolk sac, an embryonic germ is formed - the germinal shield, which first consists of an ectoblast and an entoblast, later - of three germ layers (ectoderm, mesoderm and endoderm).

The period of crushing occurs in the fallopian tube, while the fetal egg moves towards the uterus. This is facilitated by: peristaltic movements of the muscles of the tube (myosalpinx), the funnel-shaped shape of the tube, its inclination, the movement of the villi of the mucous membrane of the fallopian tube. After 6-7 days, the embryo enters the uterine cavity, where implantation takes place.

Implantation - the process of introducing the embryo into the uterine mucosa, which by this time should be in the stage of secretion. The embryo sinks into the uterine mucosa very slowly (about 40 hours) due to proteolytic enzymes produced by the trophoblast. After implantation, the functional layer of the mucous membrane thickens, which turns into a decidua, inside which the ovum develops.

The decidua (or modified functional layer of the uterine mucosa) is divided into a spongy layer and a compact layer. The compact layer consists mainly of decidual cells rich in glycogen, proteins, mucopolysaccharides, trace elements and minerals. In these cells, phagocytic processes occur and hormones (prostaglandins) are produced. The spongy, or spongy, layer consists of many overgrown glands and vessels. The egg, embedded in a compact layer, is surrounded on all sides by a decidua.

The part of the decidua between the uterus and the fetal egg is called the basal; the part covering the fetal egg from the side of the uterine cavity is called the capsular, and the rest is called the parietal. As the fetal egg grows, the capsular and parietal decidua connect, and by the fourth month of pregnancy, the fetal egg occupies the entire uterine cavity. As this process progresses, the decidua becomes thinner, except for the basal section, which thickens, vessels develop in it, chorionic villi grow into this part, forming the children's part of the placenta. In turn, the basal part of the decidua turns into the maternal part of the placenta.

Between the amniotic vesicle and the trophoblast there is a thin chord, along which an outgrowth (allantois) is formed from the posterior end of the embryo, which passes along this chord towards the trophoblast (or rather, the chorion formed from it). According to the allantois from the embryo, the vessels germinate towards the chorion.

The yolk sac in the first two months, while the placenta is not fully developed and the fetus does not have formed systems to ensure metabolism, performs very important functions. Nutrients accumulate in it, vessels, blood elements are formed, that is, the yolk sac performs the functions of extracorporeal digestion, blood circulation and hematopoiesis for the fetus. After the formation of the placenta and the most important systems and organs, the yolk sac is not needed, and it is part of the Wharton's jelly of the umbilical cord.

Development of membranes and placenta

The fetal membranes: the amnion, or water membrane, which is closer to the fetus, and the chorion, or villous membrane, which is located between the uterus and the water membrane.

The chorion is formed from the trophoblast and mesoblast. First, the villi cover the entire surface of the fetal egg, some of them melt the tissue of the decidua, forming tissue decay. Useful substances from this decay Enter through the vessels that grow into the villi of the chorion from the allantois to the fetal egg. Then the chorion, adjacent to the basal part of the decidua, grows and turns into a branched chorion, which makes up the children's part of the placenta.

On the rest of the chorion, the villi disappear, and it becomes smooth, adjacent to the decidua. Thus, the chorion is located between the decidua and the amniotic membrane.

The amnion is formed from the ectoblastic vesicle. At first it is small and located away from the embryo, but gradually the amniotic cavity increases, and gradually the amnion lines the entire chorion, the inner surface of the placenta, surrounds and covers the umbilical cord along with the yolk sac. Amnion - a thin and very strong shell - consists of a cylindrical epithelium and a connective tissue shell, in which, during the study, one can consider many layers formed from the mesenchyme: epithelial, compact, spongy; basement membrane; fibroblasts. The thickness of the shells is from 0.6 to 1.3 mm.

The fetal membranes perform the following functions: protective (mechanical protection, protection against infection), trophic, secretory, resorption, etc. The fetal membranes take part in the metabolism between the fetus and the mother. The strength and elasticity of the amnion is 5 times higher than the same qualities of the chorion.

Amniotic fluid, or amniotic fluid, fills the cavity of the fetal, or amniotic, sac. This is a complex colloidal biological medium of an alkaline reaction (pH = 7.5-8) with a specific gravity of 1.002-1.023. By the end of the first month of pregnancy, the amount of amniotic fluid is 7.5 ml, at the end of the second - 40 ml, the third - 75, the fourth - 150 ml.

In the first months of pregnancy, the trophoblast and chorionic villi take part in the formation of amniotic fluid, in later periods the water is a product of the secretion of the epithelium of the amniotic membrane, in addition, in the second half of pregnancy, the mother's plasma takes part in the exchange of amniotic fluid (filtration of fluid from the mother's blood vessels ), kidneys and lungs of the fetus. Waters are produced constantly, but even with a whole fetal bladder, their outflow from the amniotic bladder constantly occurs. Water exchange takes place every 3 hours. Reabsorption of water is carried out through the intercellular tubules of the amnion (including the umbilical cord) and the smooth chorion.

In the first months of pregnancy, the amniotic fluid is transparent, colorless, but gradually becomes cloudy due to the admixture of the discharge of the sebaceous glands of the skin, epidermis, and vellus hair. It consists of proteins, fats, carbohydrates, salts (potassium, sodium, calcium, magnesium, phosphorus, iron), enzymes, vitamins (A, B, C, PP), biologically active substances and hormones (gonadotropins, estrogens, progesterone and etc.). Amniotic fluid plays an important role in the metabolism of hormones produced by the fetoplacental complex (chorionic gonadotropin, placental lactogen, corticosteroids, progesterone, estrogens, thyroxine, etc.).

Of great importance for the life of the fetus are phospholipids, which are part of cell membranes and are involved in the formation of surfactant, which in turn provides surface tension to the lung tissue, prevents it from sticking together and the formation of atelectasis. In the study of waters, the content of phospholipids is determined. For a full-term pregnancy, the ratio of the level of lecithin and sphingomyelin is 2: 1 or more. Amniotic fluid accumulate immunoglobulins, activate blood clotting.

Amniotic fluid is of great physiological importance:

Protect the fetus from adverse external conditions (compression, temperature changes);

Protect the umbilical cord from compression;

Water is the external environment in which the fetus perfects its movements;

Swallowing water, the fetus improves the functions of the gastrointestinal tract, urinary system;

Lung tissue matures with the help of substances contained in the waters;

Bactericidal action of waters in case of infection;

Protect the uterus from active movements of the fetus;

Participate in metabolism;

The lower pole of the fetal bladder is involved in the development of labor (wedged into the area of ​​​​the internal pharynx, contributes to its disclosure);

The lower pole of the fetal bladder protects the fetal head from injury.

The decidua is not a fetal membrane, it is a modified uterine mucosa.

Placenta (placenta), or child's place. The placenta is formed from the baby and maternal parts. The children's part is formed from strongly overgrown villi of the branched chorion, the maternal part is formed from the basal part of the decidua. The placenta is about 20 cm in diameter, but may be smaller. In this case, the thickness of the placenta increases, which is usually 2-3 cm. With a smaller thickness, the diameter of the placenta increases. The total length of all villi reaches 50 km, the total surface area of ​​all villi is 10–15 m2.

The structural unit of the placenta is cotyledon - this is the name of the placental lobule formed by the villus of the first order, with the villi of the second and third order extending from it (from the Greek cotyledon - the tentacles of the polyp). According to different authors, there are 20-70 such lobules. Between the cotyledons there are septa, the central part of which is formed by the decidual tissue, and the peripheral part by the cytotrophoblast. Separate villi grow together with maternal tissues (decidua basalis) and are called fixing, or anchor. Most of the villi are located freely ("float"), they are immersed directly in the blood circulating in the intervillous space.

The surface of the villi is covered with two layers of epithelium. The outermost cover consists of a layer of protoplasmic mass without cell membranes, in which the nuclei are located; this layer is called syncytium, or plasmoidotrophoblast. On the surface of the syncytium, microvilli are located, visible under an electron microscope, further increasing the resorption capacity. Syncytium performs the most important functions of processing nutrients coming from the mother's blood, removing fetal metabolic products; it synthesizes proteins and other substances. Syncytium contains enzymes (proteolytic, lipase, diastase, amylase, etc.) that melt maternal tissues, which ensures the process of implantation and ingrowth of fixing villi into the decidua (in the early stages).

Venous blood flows from the fetus through the artery to the placenta, arterial blood enters the vein and goes to the umbilical cord.

In a normal pregnancy, the placenta is located in the upper part of the uterus, and the umbilical cord is attached to the placenta in its central part.

Functions of the placenta:

Providing the fetus with oxygen and food;

Removal of metabolic products;

Hormonal;

Protective.

The umbilical cord, or umbilical cord, connects the fetus to the placenta. The umbilical cord is formed at the site of the allantois. Outside, it is covered with an amniotic membrane. Inside the umbilical cord runs a vein through which arterial blood flows to the fetus and two arteries through which venous blood flows from the fetus to the placenta. The umbilical vessels are surrounded by jelly, a gelatinous substance that protects the vessels from compression. The umbilical cord is attached at one end to the center of the placenta (other types of attachment are types of anomalies), and the amniotic membrane of the umbilical cord passes into the amniotic membrane covering the placenta. The other end of the umbilical cord enters the region of the umbilical ring in the abdominal wall of the fetus.

The length of the umbilical cord at the end of pregnancy is about 50-60 cm, the diameter is about 1.5 cm.

The placenta is called the placenta along with the membranes and the umbilical cord after they are released at the end of childbirth.

Fetal physiology

The embryonic, or germinal, period lasts the first 8 weeks, after which the fetal, or fruiting, period begins, which lasts until the birth of the child. During the embryonic period, the rudiments of all organs and systems are formed. Damaging factors affecting the body of a pregnant woman at this time can lead to the death of the embryo or abnormalities in the development of organs.

In the fetal period, there is a further development of organs and systems, so the harmful effects are undesirable even after the completion of embryogenesis, especially in the first half of pregnancy.

The cardiovascular system. The heart and blood vessels are formed from the mesoderm. At three weeks of pregnancy, the heart looks like a contracting tube, and by 8 weeks it resembles a human four-chambered heart in structure. In the interatrial septum, an oval hole remains open to drain blood from the right to the left atrium. This is necessary because before the birth of a child, the pulmonary circulation does not function in him and blood should not enter the lungs through the pulmonary trunk. The reverse flow of blood from the left atrium to the right is impossible due to a special valve. The foramen ovale closes after the birth of the child.

The first vessels are formed extracorporeally in the yolk sac at the end of the 2nd week, but by the 5th week the vessels are laid in each organ.

The heart rate in the first weeks is 90-130 bpm. At 7-15 weeks, the heart accelerates its work and the contraction rate is 150-170 beats / min, in the second half of pregnancy and in childbirth, the heart rate of a healthy fetus is 130-145 beats / min.

Fetal circulation. Blood enriched with oxygen and nutrients enters the fetus through the vein of the umbilical cord. In the fetal body, the umbilical vein goes to the inferior vena cava, from which a branch for the liver is taken, since the liver needs fresh arterial blood, active processes take place in it, including hematopoiesis. The section of the umbilical vein from the umbilical ring to the inferior vena cava is called the arachnoid duct. Blood from the inferior vena cava, enriched with oxygen, enters the right atrium, and blood from the superior vena cava, which contains carbon dioxide, also enters there. To prevent these two streams from mixing, they are separated by a special Eustachian valve (valve of the inferior vena cava). Thanks to her, blood from the inferior vena cava is directed through the interatrial foramen ovale into the left atrium, then into the left ventricle and into the aorta. Venous blood from the superior vena cava enters the right ventricle and then into the pulmonary trunk.

Since there is no gas exchange in the lungs of the intrauterine fetus, almost all the blood is discharged through the batallian duct into the descending aorta. In a newborn baby, the batallian duct should not function. (In case of non-closure of the batallian duct, surgical intervention is required). The ascending branch of the aorta is more supplied with oxygen, supplies the upper half of the body, upper limbs, and the head, which develops more intensively. The descending aorta has an admixture of venous blood, supplies blood to the lower body and lower limbs, which develop more slowly. After metabolism and gas exchange, venous blood flows through two arteries through the umbilical cord to the placenta to be enriched again with oxygen and nutrients.

Hematopoiesis. The functions of hematopoiesis up to 12 weeks are performed by the yolk sac, from 13 to 28 weeks, blood elements are produced in the spleen, liver, after which the spinal cord takes over the functions of hematopoiesis. Erythrocytes appear in the blood at 7-8 weeks. Fetal hemoglobin has an increased ability to absorb oxygen.

The fetal respiratory system begins to form early, although it does not function during pregnancy as it does in a newborn. External respiration of the intrauterine fetus is carried out through the placenta. The rudiment of the respiratory system appears at the end of the 4th week. Month after month, the bronchial tree is formed, which is basically already developed by 6 months and improved until birth.

The lungs of the fetus first have a glandular structure containing fluid, its excess is swallowed by the fetus and enters the amniotic fluid. The lungs make respiratory movements, but with the glottis closed, so that the amniotic fluid does not enter the lungs. Excursions of the lungs contribute to the development of the lungs themselves and the respiratory muscles, facilitate the work of the heart.

The epithelium of the airways produces a liquid secret that covers the bronchi and alveoli. In order for the lungs to expand, towards the end of pregnancy, the alveoli are covered with a thin film of lipoproteins called surfactant, which contributes to normal lung function. The main component of this substance is lecithin. Up to 6 months of intrauterine development, surfactant is absent, from 7 months its production is activated, but up to 36 weeks its amount may not be enough to ensure normal breathing. Therefore, premature babies often develop pneumonia, with severe prematurity, lung atelectasis develops, respiratory failure, which, without special treatment, can lead to death. The production of surfactant depends on the function of the adrenal glands, phospholipid metabolism. This substance is found in the amniotic fluid, from which an artificial surfactant is made to treat premature babies.

The nervous system is formed from the ectoderm. First, a groove is formed, then a tube, in the upper part of which thickenings and bends are formed. From the upper part then the brain is formed. The nervous system develops and improves throughout pregnancy, so harmful effects during pregnancy, even late in pregnancy, can lead to pathology of the nervous system.

The endocrine system of the intrauterine fetus is actively working. Some organs are formed and manifest themselves very early - during embryogenesis, others appear closer to the middle of prenatal age. The rudiments of the endocrine glands are formed already in the 2nd month, hormones begin to be synthesized already by the middle of pregnancy. The function of the endocrine glands of the fetus is influenced by the hormones of the pregnant woman, and. on the contrary, the hormonal activity of the fetus affects the metabolism of the mother.

The immune system. Immune reactions are due to the activity of the thymus gland, which is formed at the 6-7th week of pregnancy. This is where lymphoid cells mature. Some lymphocytes migrate to peripheral lymphatic structures (lymph nodes and spleen). Immunologically active proteins are formed in the bone marrow from 3 months. Immunoglobulins are synthesized during the prenatal period, but not actively enough. In the second half of pregnancy, the activity of the spleen in relation to leukopoiesis increases, but the activity of leukocytes and lymphocytes is insufficient. In response to the introduction of infection, there is no inflammatory reaction, and dystrophic changes immediately appear. Antibodies against pathogens of certain diseases can pass to the fetus from the mother, thus forming passive immunity. The thymus gland reaches its maximum development by the end of the intrauterine period, but after birth, it involution occurs, since other structures begin to actively perform the immune function. Activation of immunity occurs after birth due to the influence of exogenous factors.

excretory system. The excretory function of the fetus is provided mainly by the placenta, however, the urinary excretory system of the fetus begins to function early. The kidneys begin to form at the 2nd month of pregnancy, they are fully formed by 32-34 weeks of intrauterine development. Urine is formed already at the end of the first half of pregnancy, by the end of pregnancy the amount of urine is about 50 ml per day. The fetus swallows amniotic fluid, part of the fluid is removed through the placental system, part is filtered by the kidneys in the form of urine, which is released into the amniotic fluid. But the urine of the fetal fetus is not like the urine of a child, since the excretory function is mainly provided by the placenta, in addition, the amniotic fluid is cleaned due to the activity of macrophages of the aquatic membrane and is constantly updated.

Digestive system. The nutrition of the fetus in the period of early embryogenesis before the implantation of the fetal egg is carried out at the expense of internal reserves. Further, through the villi of the chorion, nutritious products come from the reserves of the mucous membrane (from the so-called tissue decay). The supply of nutrients accumulates in the yolk sac, which provides the functions of external digestion until the digestive and circulatory organs are fully functioning. After the formation of the placenta, the nutrition of the fetus is carried out mainly due to the intake of nutrients through the placenta, metabolic products are removed through it. The organs of the gastrointestinal tract are formed from the endoderm.

The fetal liver functions very actively, participating in hematopoiesis, the formation of enzymes, bile, and metabolism. The fetus swallows amniotic fluid, the liquid part is absorbed to a greater extent, and the dense part is part of the meconium. This improves the function of the gastrointestinal tract. Meconium consists of water, bile, vellus hair, skin scales, fatty lubricant, is a yellowish-greenish mucus-like mass. Since the metabolism is provided by the placenta, intrauterine ingestion of water is necessary mainly for training the kidneys and digestive tract. With insufficient cleansing function of the amnion, the water may have a greenish color.

Sexual system. The formation of the genital organs begins at the end of the 2nd month, at the end of the 3rd month differences in the genitals in boys and girls are noticeable, the final formation ends by the end of the 4th month. The pituitary and gonads are formed already in the first trimester, hormonal sexual differentiation occurs starting from 16 weeks, at 20 weeks the formation of germinal follicles is already observed.

Growth and weight of the fetus at different stages of pregnancy. The height and weight of the fetus depend on genetic data, it is necessary to know with what weight and height the parents were born, to take into account the actual anthropometric data of the parents, in multiparous fetuses the weight of the fetus is greater than in primiparas. Fetal growth depends on growth hormone. Affects the weight and growth of the fetus insulin, providing an anabolic effect. In diabetes, the mother's sugar level is elevated, in connection with this, the production of insulin in the fetus increases, which causes its macrosomia.

The length is determined by the Haase formula. The length of the fetus from the 1st to the 5th month is equal to the number of the month squared, and from the 5th to the 10th month is equal to the number of the month multiplied by 5. Knowing the length of the fetus, you can calculate the approximate gestational age. For example, the length of the fetus is 40 cm. According to the inverse Haase formula, dividing 40 by 5, we get 8, i.e. 8 months of pregnancy. Multiplying 8 by 4, we get 32 ​​weeks of pregnancy.

This is especially important in the case when a woman did not follow her menstruation, was not examined during pregnancy, and the gestational age in case of late treatment is not very accurately determined. The weight of the fetus by the end of the first trimester is very small, about 20-25 g. By the end of the first half of pregnancy it is 300 g. The fetus reaches a weight of 1 kg by 28 weeks and 2.5 kg by 36 weeks.