Causes of the birth of labor

, medical expert
Last reviewed: 19.10.2021

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The causes of the birth of labor have not been studied sufficiently to date. We have given the leading causes of the birth of labor.

The role of the central nervous system

The main role in the preparation of the woman's organism for childbirth belongs to the central nervous system. With its help, all the physiological processes occurring in the pregnant body, including the delivery process, are directed and maintained at an appropriate level.

Particular attention should be paid to two physiological phenomena - the conditioned reflex and dominant.

The dominant is the temporarily dominant reflex "physiological system" that directs the work of the nerve centers at the moment. The dominant focus can be localized in the spinal cord, in the subcortical structures or in the cerebral cortex; therefore, the primary focus distinguishes the spinal dominant, subcortical or cortical.

The dominant is formed as a reflex physiological system necessarily with a primary focus in one of the sections of the central nervous system. The focus of persistent excitation in the central nervous system can be created not only by a reflex path, but also under the influence of hormones.

In obstetric practice, a number of scientists formulated the principle of a generic dominant. An uncomplicated course of pregnancy and fetal nurturing is facilitated by the presence of the gestational dominant. Changes related to pregnancy and childbirth concern the whole organism, therefore the concept of "generic dominant" unites in one dynamic system both higher nervous centers and executive bodies. According to the changes occurring in the reproductive apparatus, it is possible to fairly accurately judge the formation of the so-called "peripheral link" in the women of the generic dominant.

In the offensive and deployment of the clan act, the internal impulses that emanate from the fetal egg and the pregnant uterus play a major role. In order for the uterus to regularly contract, it must be provided, on the one hand, with its "readiness", and on the other hand, appropriate regulation by the central nervous system.

On the basis of the data given, it can be concluded that the expression "the biological readiness of a woman for childbirth" is essentially identical with the notion of a "generic dominant".

Psychological readiness of a woman for childbirth

Modern obstetricians attach great importance to the psychological state of women immediately before and during the birth, since the physiological course of the birth act largely depends on it. As a matter of fact, the method of physiopsychoprophylactic preparation of a pregnant woman for childbirth developed by domestic authors and received worldwide recognition is aimed at creating an optimally expressed psychological readiness for childbirth.

A number of works suggested psychological aspects of the therapeutic measures of the program for the preparation of women for childbirth, and in these cases, through the reduction of emotional stress, improvement of the fetus condition and faster adaptation of newborns in the first days of the child's life are noted. We studied the features of the state of newborns (neurological examination, electromyography, quantitative determination of muscle tone) in groups of pregnant women who had received psycho-preventive training and had not passed it. At the same time, the state of newborns was significantly better in the group of pregnant women who had received psycho-preventive training. The number of positive assessments of the state of children on the Apgar scale is increasing, their clinical characteristics are close to those in the group with normal delivery. The same can be said about the chronometric, tonometric and electromyographic characteristics. Hence, a conclusion can be made about the powerful therapeutic effect of psycho-prophylaxis on the condition of the fetus and newborn baby. However, improvement in the motor sphere appears to be secondary because of an improvement in blood supply and a decrease in sensitivity to the hypoxic stressor in childbirth, since changes in the functional structure of the reflexes, when using psycho-preventive preparation during the normal course of the birth act, could not be detected.

Changes in the state of consciousness associated with physiological births

Described unusual psychic phenomena that arise during physiological births. The most frequent were the subjective sensations of "the unusualness of one's own mental processes" (42.9% in childbirth and 48.9% after childbirth), an unusually deep experience of happiness or grief (39.8% and 48.9%, respectively), "almost telepathic contact with (20.3 and 14.3%) or the same contact with relatives and husband (12 and 3%), panoramic experiences of lived life (11.3 and 3%), as well as the phenomenon of "disconnection" from what is happening and observation with them from the side (6.8 and 5.3%).

In the postpartum period, 13.5% of patients had unusual experiences related to sleep: the difficulty of falling asleep with the emergence of an uncontrolled flow of thoughts, the "play" of various life situations, the previously missing colored dreams, the difficulties of spilling, nightmares, etc.

There are no analogues of the described phenomena in the literature, however, individual phenomena were observed by different researchers in healthy people who are in unusual conditions of existence, for example, in sensory deprivation, tense and life-threatening work, work in a "hot" shop, with natural disasters, and also with some modern forms of psychotherapy or with periterminal states.

Many authors believe that in such conditions, healthy people develop changes in consciousness. This position is shared by us, and under the changes of consciousness we mean a kind of consciousness of a healthy person who is in unusual conditions of existence. In our observations, such conditions of existence were physiological genera.

So, almost half of the studied patients under physiological births observed psychic phenomena, which are unusual for their daily routine life.

Phenomena, therefore, arise involuntarily (unconsciously) and the patients themselves are characterized as unusual for them. However, the moles, who experienced such experiences at the first birth, consider them "normal", usual for delivery and readily report them.

It is generally believed that childbirth is a physiological act, to which the mother's organism is evolutionarily prepared. However, at the same time, this process is the formation of perinatal matrices, that is, stable functional structures that persist throughout life and are the basis for many mental and physical reactions. The literature contains a lot of factual data, which allows us to state that the hypothesis about the formation of perinatal matrices has become an original theory.

The main perinatal matrices that are formed in childbirth correspond to the periods of childbirth:

  • the first matrix is formed at the beginning of the first stage of labor;
  • the second - with intensification of labor claws when opening the uterine pharynx 4-5 cm;
  • the third - in the II period of childbirth when the fetus passes through the birth canal;
  • the fourth at the time of the birth of the child.

It is shown that the formed matrices are an integral part of human reactions in everyday life, but in some cases, for example, with considerable neuropsychic load, in a number of diseases, traumas, etc., they can be activated and determine the reaction of a person in whole or in part. Activation of matrices leads to the strengthening of natural, evolutionarily developed and strengthened mechanisms of physiological protection and recovery. In particular, when treating neuroses during psychotherapy sessions, altered states of consciousness arise, the phenomenology of which allows us to determine which matrix is activated and which matrix activation is most effective for therapy. Along with this, we believe that an active waking consciousness prevents the inclusion of physiological mechanisms of recovery, and a change in consciousness is a physiological response that provides the optimal level for inclusion of these natural mechanisms of recovery.

Figuratively speaking, nature took care of the human psyche and under unusual conditions of its existence, the level of the conscious in the psyche changes, causing unconscious forms of psychic reactions that, by analogy with the "architopes" of CG Jung, can be called "arch-consciousness."

What has been said about matrices relates to one part of the "mother-fetus" system - the fetus and the child being born, but this also applies to the other part - the mother.

During the childbirth and the postpartum period, the mother's organism reacts with known mental and physical reactions, but primarily with the activation of her own perinatal matrices and, in particular, with a change in consciousness.

Thus, the psychic phenomena described in physiological births, we tend to understand as manifestation of the activation of the ancient mechanisms of the mental, as "arch-consciousness".

Like any ancient mechanism of the psyche, the "arch-consciousness" contributes to the inclusion of evolutionarily developed nonspecific reserve mechanisms of health in general and recovery, in particular. Such mechanisms are suppressed by an active waking consciousness.

Role of kallikrein-kinin system

Kallikrein-kinin system (CCS) is a multifunctional homeostatic system, which by the formation of quinines is included in the regulation of various functions, in particular, the functions of the reproductive system of the body. Kallikreins are serine proteases releasing kinins from substrates present in the plasma, called kininogens. Kallikreins are divided into two main types: plasma and glandular. There are also two main forms of the substrate kallikreina - kininogens with low and high molecular weight, present in the plasma. Plasmatic kallikrein, also called Fletcher's factor, releases kinins from high molecular weight kininogen, which is also known as the Fitzgerald factor. Plasmatic kallikrein is mainly in an inactive form (precalcrerein) and, together with high molecular weight kininogen and factor Hageman, is included in the blood coagulation mechanism, activating factor XI. This system takes part in the activation of plasminogen with its transformation into plasmin, as well as in the body's reactions to damage and inflammation.

The activity of the kallikrein-kinin system increases during a normally occurring pregnancy and is one of the important factors in the onset of contractile activity of the uterus during childbirth. It is also known that with the activation of the kallikrein-kinin system, a number of disturbances in the course of pregnancy and childbirth are associated.

Suzuki and Matsuda (1992) studied the connection between the kallikrein-kinin system and blood coagulation systems in 37 women during pregnancy and childbirth. The most clearly revealed changes in the function of the kallikrein-kinin system. Prekallikrein rapidly declines from 196.8% in late gestation to 90.6% at the onset of labor. This causes changes in the coagulating and fibrinolytic blood systems and affects the onset of contractions of the uterus with the onset of labor. The interrelation of bradykinin receptors and the mechanism of delivery is shown. Takeuchi (1986) conducted a study of bradykinin receptors in contraction of the uterine muscle. The study of receptors was carried out in various tissues: in the pregnant uterus of rats, in the chorionic membrane and placenta of women. A specific receptor is found in the chorionic membrane of women and the uterus of rats. The receptor is located on the plasma membrane. The association constant and the maximum binding ability of the receptor were the lowest in the uterus of rats on the 15th day of pregnancy, they increased during labor.

In experiments in Wistar rats, the activity of kininogenase was detected in the uterus, vessels of the placenta, amniotic fluid and membranes. Kallikrein-like enzymes were both active and, mainly, in an inactive form. Lana et al. (1993) conclude that kallikrein-like enzymes can be directly involved in the processes of polypeptide hormones and indirectly - through the release of kinins - into the regulation of blood flow during pregnancy and childbirth.

According to NV Strizhova (1988), the high activity of kininogenesis processes is important in the pathogenesis of hypoxic disorders of the fetus and the newborn caused by late toxicosis of pregnant women, chronic inflammatory diseases of the mother, which determines the violation of the rheological properties of blood, tone and vascular permeability. As the severity of asphyxiation deepens, the adaptation mechanisms fail, including intense and unbalanced hyperinfection of kininogenesis. Clinical and experimental substantiation of the use of the bradykinin-parmidin inhibitor in obstetric practice was carried out. The role of the kallikrein-kinin system in the onset of labor was established, and the use of parmidin is indicated in the treatment of violations of the contractile function of the uterus during pregnancy and childbirth and improves the functional state of the fetus, and reduces pain in labor. Probably, this is due to the fact that one of the causes of angina pain with stable angina is hyperproduction of kinins and irritation of pain receptors of the heart.

The value of catecholamines

Catecholamines are represented in the animal body by three derivatives that consistently turn into each other from Dopa to dopamine, then into norepinephrine and adrenaline. The adrenaline and norepinephrine are retained in the adrenal glands.

Paraganglia are producers of norepinephrine (rather than adrenaline) and provide local supply of catecholamines of nearby organs and tissues.

The physiological effects of catecholamines are diverse and affect virtually all body systems.

Under the influence of sex hormones, the level of norepinephrine in the uterus changes. This distinguishes the adrenergic nerves of the genital organs from other sympathetic neurons, while short neurons are more prone to the action of sex steroids than long ones. Thus, the administration of estradiol leads to an increase in the content of noradrenaline in the uterus, vagina, oviducts in different animal species. In humans in the body and cervix, adrenaline and acetylcholine lead to an increase in contractions.

In the last days of pregnancy, only a small amount of norepinephrine can be found in the uterus. The decrease in the content of noradrenaline in the uterus, according to a number of authors who conducted experiments on guinea pigs, rabbits, dogs, in humans, has the character of protection from feto-placental ischemia during generalized sympathetic activation in the mother.

Changes in the content of catecholamines in the uterus of the rat at different periods of pregnancy, childbirth, and the postpartum period have been revealed. A characteristic feature of adrenergic innervation is a decrease in the intensity of fluorescence, which indicates a decrease in the number of adrenergic fibers. In addition, we studied the contractile activity of the myometrium and the level of catecholamines in the blood during physiological and pathological births. It is shown that adrenaline stimulates the contractile activity of the nonpregnant uterus and inhibits spontaneous labor activity, while norepinephrine causes contractions of the pregnant uterus. It can be assumed that a decrease in the amount of adrenaline and an increase in the content of norepinephrine in the uterus is one of the mechanisms that induce the onset of labor. Thus, with the weakness of labor, the content of adrenaline in the blood plasma did not differ significantly from that in normal births, while the content of norepinephrine was almost half that of healthy women giving birth. Thus, if the motor function of the uterus is disturbed with a weak labor activity, a decrease in the concentration of catecholamines is revealed, mainly due to norepinephrine. If we draw an analogy of the ratio of adrenaline: norepinephrine in the myocardium, then those effects are favorable for the heart, as a result of which the concentration of adrenaline in the myocardium decreases, and the concentration of norepinephrine slightly increases. These changes reflect, apparently, an increase in the ability of the body to adapt to high demands that arise not only in muscular work, but also in other situations. Conversely, an increase in the level of adrenaline in the myocardium and a decrease in the level of norepinephrine testify to unfavorable changes in the functional state of the heart, a decrease in its adaptive capacity, and also cause various disturbances in its work. Therefore, the ratio of adrenaline: norepinephrine in the myocardium is an important physiological constant. Zuspan et al. (1981) found that the uterine concentration of norepinephrine and adrenaline in hypertensive forms of toxemia is higher than in normal pregnancy; this indicates the important role of catecholamines in the etiology and maintenance of hypertension. These data are confirmed by modern research - in severe nephropathy, the content of noradrenaline in the myometrium of the uterine body and the lower segment at the end of pregnancy and in labor is 30% higher than in uncomplicated pregnancy.

The role of endocrine factors

During pregnancy and childbirth there is a reorganization of the function of all the endocrine glands of a woman. Along with this, there is an increasing activity of the glands of internal secretion of the growing fetus. A huge role is played by the specific gland of pregnant women - the placenta.

The data of modern literature indicate that estrogen, progesterone, corticosteroids and prostaglandins belong to the most important hormones involved in hormonal changes in the body of pregnant women, which largely determine the characteristics of the course of pregnancy and childbirth. However, recent studies have shown that progesterone and estrogens play only a supporting role in the onset of labor. However, in sheep and goats before birth, the lowest concentration of progesterone in the blood plasma is established and the level of estrogens rises. Some authors have shown that a woman has estradiol: progesterone before delivery increases and this has a direct etiological relationship to the onset of labor.

It has also been established that catechol estrogens, which are the main metabolites of estradiol, increase the formation of prostaglandins in the uterus even more than the original compound.

It is shown that the content of catechol estrogens in the blood of the umbilical artery and the umbilical vein is higher for physiological labor than for elective caesarean section. The role of catechol estrogens in the synthesis of prostaglandins and in the potentiation of catecholamines through competing inhibition of catechol-O-methyl transferase is important, showing that catechol-oestrogens can play an important role in triggering involvement in the onset of labor and delivery in humans. Catechol estrogens also potentiate the lipolytic effect of epinephrine in the release of arachidonic acid from phospholipids. At the same time, there were no clear changes in the level of estradiol and progesterone in the peripheral blood before the onset of spontaneous labor. Earlier, the content of steroid hormones and Ca 2+ ions in the blood serum was studied in 5 groups of pregnant and parturient women: pregnant women with a period of 38-39 weeks, parturients at the beginning of labor, pregnant women with a normal and pathological preliminar period. To clarify the dependencies existing between steroid hormones, we performed a correlation analysis. Correlation was detected in the normal preliminar period between progesterone and oestradiol. The correlation coefficient is 0.884, the probability is 99%. By the time of birth, the correlation dependence in the same group is lost. Antigestagens in recent years are increasingly used to abort pregnancy in the early stages. Antigestagens dramatically increase the contractile activity of the uterus and therefore can be used for the purpose of childbirth both separately and in combination with oxytocin.

The role of hormones in the adrenal glands of the fetus

The exact value of adrenal hormones in the birth of the fetus is not established, but it is believed that they also have an auxiliary value. In the last decade, the role of the adrenal glands in the fetus has been shown to overstate pregnancy and the onset of normal labor. In the experiment it was found that in some animals in the last 10 days of pregnancy adreno-cortical activity of the fetus increases and reaches a maximum on the day of childbirth. In women who undergo cesarean section surgery under full-term pregnancy, but without labor, the concentration of cortisol in the umbilical cord blood is 3-4 times lower than in women with physiological labor. The level of corticosteroids in the umbilical artery becomes maximum at the 37th week of pregnancy, when the fetus reaches maturity. Cortisol and progesterone are antagonists in both the blood plasma and the uterus. Fructose cortisol has a depressing effect on progesterone and thus stimulates the activity of the myometrium. In addition, cortisol increases the activity of estrogen and prostaglandin F2a in the placenta.

A great role of adrenal glands in the development of labor is recognized by many authors. The adrenal glands of the mother play a lesser role. The mechanism of action of cortisol is not limited to "enzymatic" maturation of the fetus (for example, its lungs). Fetal corticosteroids penetrate into the amniotic fluid, the decidual membrane, occupy the receptors of progesterone, destroy the cell lysosomes and increase the synthesis of prostaglandins, which can lead to the onset of labor.

An increase in the synthesis of estrogens in the third trimester of pregnancy is naturally associated with an increase in the synthesis of dehydroepiandrosterone by the adrenal glands of the fetus. In the placenta, estrogens are synthesized from the latter through a series of links, which increase the synthesis of actomyosin and increase the number of oxytocin receptors in myometrium. An increase in the concentration of estrogens in the amniotic fluid is accompanied by an increase in the synthesis of prostaglandins.

The role of oxytocin

Oxytocin (OK.) Is formed in large cell nuclei of the hypothalamus, descends along the axons of hypothalamic neurons and is stored in the posterior lobe of the pituitary gland.

As you know, the causes of the birth of labor remain insufficiently studied. Great importance is attached to the role of catecholamines and prostaglandins in the unleashing of labor.

It is important to take into account that in the posterior lobe of the pituitary, there are huge reserves of oxytocin, much larger than necessary to provide normal physiological functions, and the synthesis of the peptide is not always directly related to the rate of its release. In this case, the newly synthesized hormone is subjected to a preferred secretion.

Significant stocks of oxytocin in the pituitary gland can play an important role in emergency conditions, for example, during labor during fetal expulsion or after blood loss.

At the same time it is rather difficult to determine the content of oxytocin in blood plasma by the standard radioimmunological method, besides this approach does not provide the time resolution necessary for the evaluation of electrical phenomena that can last for only a few seconds.

At the same time, when studying the central regulation of oxytocin, we do not know anything about how explosion-like increases in electrical activity are generated in oxytocin-synthesizing cells or about what determines the interval between successive periods of increased activity. A lot is known about neurotransmitters emerging along the nerve pathways and participating in the stimulation or inhibition of the release of oxytocin. In this case, the neurotransmitters act directly near the synapse, and do not circulate in the brain.

In this regard, the issue of basal secretion of oxytocin is important. It is believed that the physiological significance of basal levels of oxytocin in the blood plasma and the changes that can occur with them are not determined.

Oxytocin is one of the most powerful of all uterotrophic agents. However, being a powerful activator of uterine contractions, its strength depends not only on the properties of oxytocin, but also on the physiological state of the uterus. Thus, the concentration threshold required for stimulation of the estrogenized uterus in rats under in vitro conditions is 5-30 μED / ml, and for human myometrium in full term, 50-100 μDU / ml. In molar concentrations, these levels correspond to 1-5 × 10 11 and 1-2 × 10 10, respectively. Based on these data, it can be argued that there are currently no other oxytochemicals reaching such a force on the myometrium.

It is important at the same time to note that the human uterus in labor in vivo is even more sensitive than in vitro; the effective levels of oxytocin in the blood plasma were doses less than 10 mC / ml (<2 • 10 10 M). Modern studies have also shown that the sensitivity of human myometrium in the process of childbirth is 1-4 mUED / ml. In a comparative aspect, prostaglandin F 2a has only 1/3 of the oxytotic activity of the rat uterus in vitro. At termed pregnancy in humans, the threshold dose of prostaglandin F 2a and prostaglandin E2 is approximately 3 orders of magnitude higher than oxytocin.

Oxytocin levels in the mother. To determine the levels of oxytocin in childbirth and at the time of delivery, many studies have been devoted and only a small number of studies have identified oxytocin in pregnancy.

Earlier, attempts were made to determine oxytocin in biological media of the human body by a biological method. However, these methods, obviously, were not very adequate, as they gave a wide spread of digital data on the content of oxytocin in the biological environment of the human body. At present, new approaches have been developed to radioimmune determination of the concentration of oxytocin in biological media. It has been established that uterine sensitivity clearly rises as pregnancy progresses, but oxytocin levels in the blood are simultaneously too low to stimulate uterine contractions.

With the development of radioimmune methods, a series of studies based on large contingents of pregnant women at various stages of pregnancy became possible.

In most studies in blood plasma, using the radioimmunoassay during pregnancy, oxytocin is determined and, as pregnancy progresses, its concentration increases.

A study was also made of the levels of oxytocin at different periods of labor by the radioimmune method. Most researchers noted the fact that in childbirth levels of oxytocin in the blood plasma are higher than in pregnancy. This increase is not very significant compared with the level of oxytocin in pregnancy. Oxytocin levels in the first stage of labor are slightly higher than levels of oxytocin at the end of pregnancy. At the same time, they reached a maximum in II and then declined in the third stage of labor. Oxytocin levels in the spontaneous emergence of labor are significantly higher than in a full-term pregnancy without labor. At the same time, there were no significant changes in the level of oxytocin during the entire I period of labor. It can be assumed that oxytocin circulating in the mother's blood is oxytocin of pituitary origin, although immunoreactive oxytocin was detected both in the human placenta and in the ovaries. At the same time, in a number of studies it has been established that in animals during delivery there is a significant decrease in the level of oxytocin in the posterior lobe of the pituitary gland. What happens in a person remains unknown.

At present, two methods for the determination of oxytocin in blood plasma have been developed using two antisera to it. With intravenous administration of synthetic oxytocin in healthy women, a linear relationship between the dose of administered oxytocin and its level in the blood plasma (1-2 mU / ml) was revealed.

Oxytocin levels in the fetus. In the first studies on the definition of oxytocin, it was not possible to determine oxytocin in the mother's blood, while in the blood of the fetus its high levels were noted. At the same time, a distinct arteriovenous difference in its content in the umbilical cord was revealed. Therefore, a number of authors believe that birth is caused more fruit than maternal oxytocin. It is also important to note that in pregnancy oxytocinase regulates the level of oxytocin in the blood, while oxytocinase activity in fetal blood serum is not revealed, which indicates that this enzyme does not go into the fetal circulation system. Many researchers have shown that levels of oxytocin in the umbilical artery are higher than in the venous blood of the mother. This gradient and arteriovenous difference in the umbilical cord give reason to assume about the transition of oxytocin through the placenta or rapid inactivation of oxytocin in the placenta. The placenta contains an aminopeptidase that can inactivate oxytocin (and vasopressin) and thus the fate of oxytocin extracted from the umbilical cord blood is unknown. However, when oxytocin is injected into the mother's bloodstream to induce labor, the arterio-venous difference in oxytocin reverses by rolling that the oxytocin transition through placenta is possible. The transition of oxytocin from fetus to mother is shown in experimental studies in baboons. The arterio-venous difference of 80 ng / ml is observed in spontaneous spontaneous births, and the flow of blood through the placenta is 75 ml / min and the transition of oxytocin to the mother is about 3 meads / ml, i.e., the amount of oxytocin that is sufficient to induce an ancestral activities. In this case, a high arteriovenous difference is revealed both in spontaneous labor and in cesarean delivery in childbirth. There was also an increase in the level of oxytocin in the fetal blood of those women whose labor began earlier than the expected planned caesarean section, indicating an increase in fetal oxytocin during the precursors or in the latent phase of labor.

At autopsy in fetuses and newborns it was found that at 14-17 weeks of pregnancy the content of oxytocin in the fetus is 10 ng, and in newborns - 544 ng. There is, thus, a 50-fold increase in the content of oxytocin from the beginning of the second trimester until birth. Assuming that the content of oxytocin in the pituitary gland at the beginning of labor is not less than 500 ng (equal to 250 honey), this amount is sufficient for the transition to the mother of 3.0 mCED, which can cause the onset of labor. Immunoreactive oxytocin with full biological activity can be extracted from the human placenta after spontaneous physiological delivery. This shows that the placenta does not destroy oxytocin as quickly as before, at least not during and after childbirth. Perhaps this can be explained by the fact that prostaglandins of the E1, E2 and F2a series, which are formed in the placenta mainly during labor, inhibit the activity of placental oxytocinase.

In the anencephaly of the fetus oxytocin is not formed, in the hypothalamus and, with the exception of its essential secretion by the gonads, it is possible to expect low levels of oxytocin in fetal blood plasma, although the possibility of oxytocin diffusion from the mother can not be ruled out.

Amniotic fluid contains sufficient amounts of oxytocin, which can be determined in both pregnancy and childbirth. In this case, oxytocin, located in the amniotic fluid, can achieve decidua (a falling shell) and myometrium by diffusion through the intracellular channels in the membrane. The fetus also secrets a significant amount of vasopressin. In this case, the arteriovenous difference in the umbilical cord and the difference between the maternal and fetal vasopressin are significantly greater than oxytocin. Although vasopressin has a lower oxytocic effect than oxytocin on the pregnant female uterus, fetal vasopressin can enhance the effect of oxytocin. The secretion of vaeopressin is stimulated by fetal distress and fetal vasopressin can thus be of particular importance in the etiology of premature birth. At the same time, little is known about the oxytotic effect of vaeopressin on the human uterus in term of full term pregnancy.

Hypoxia stimulates the release of oxytocin in the fetus and, thus, stimulates uterine activity and accelerates labor with fetal distress. However, this hypothesis requires further research. In a modern work Thornton, Chariton, Murray et al. (1993) emphasizes that although most authors acknowledge that the fetus forms oxytocin, a number of researchers do not believe that the fetus affects delivery through the release of oxytocin. Thus, in the case of anencephaly the fetus does not form oxytocin, although the labor and the level of oxytocin in the mother were normal; the transition of fetal oxytocin into the blood circulation system of the mother is unlikely, since the placenta has a high activity of cystinamine peptidase, which actively destroys oxytocin; the progress of normal delivery does not correlate with any measurable increase in oxytocin in the blood plasma of the mother; the fetus did not have cystinamine peptidase activity in the blood plasma; Analgesia in the mother can affect the release of fruit oxytocin.

The fetus can stimulate the uterus, releasing oxytocin towards the placenta or penetrating the myometrium through the amniotic fluid. This possibility requires further investigation, since reports of the concentration of oxytocin in the amniotic fluid are contradictory. The decrease in the formation of oxytocin in the fetus is not associated with the use of pethidine (promedol) in childbirth. This is surprising, since the release of oxytocin from the posterior lobe of the pituitary gland in animals is inhibited by endogenous opioid peptides or opiates, and the effect of which is reversed by naloxone. At the same time, the formation of oxytocin in the fetus was increased after the application of epidural analgesia. In contrast to some studies, it has been shown that fetal oxytocinum in caesarean section does not increase at the onset of labor and this is convincing evidence, in the opinion of some authors, that fetal oxytocin does not affect uterine activity, in addition, fetal oxytocin release does not increase with the onset of labor or in the presence of acidosis in the fetus. These data require further research.

Thus, we can draw the following conclusion about the role of oxytocin as the cause of the onset of labor:

  • Oxytocin is the most potent uterotrophic drug in pregnancy and in childbirth in humans;
  • oxytocin is secreted by the mother and the fetus in quantities that have physiological activity, provided that the myometrium reaches a high sensitivity to oxytocin, necessary for the onset of labor;
  • the sensitivity of the uterus to oxytocin is determined by the concentration of specific oxytocin receptors in myometrium;
  • the neurohypophysis of the fetus contains a significant amount of oxytocin;
  • the concentration of oxytocin in the umbilical artery is higher than in the umbilical vein and venous blood of the mother combined, indicating a fecal secretion of oxytocin in labor and the disappearance of oxytocin from the fetal blood plasma as it passes through the placenta;
  • the decaying shell (decidua) contains the same amounts of oxytocin as the myometrium.

The importance of prostaglandins

Prostaglandins (PG) in the uterus play an important role, as a factor necessary for the preservation and development of pregnancy in its various terms. At present, the phenomenon of antagonism between PGF2a and chorionic gonadotropin (HG), which is the main mechanism in the preservation of pregnancy, has been identified. If this antagonism is disrupted, then the tendency to decrease the chorionic gonadotropin and increase the level of the GHF 2a begins, with the subsequent development of a threatening and started abortion. With the introduction of large doses of chorionic gonadotropin in women with the threat of termination of pregnancy, an increased level of PGF 2a can be reduced.

In recent years, there have been reports that have expanded our knowledge of the preliminary link of prostaglandin synthesis and proposed new hypotheses for the onset of labor. In 1975, Gustavii proposed the following theory of the onset of labor: under the influence of changes in the level of estrogens and progesterone, changes occur in decidual lysosomes, enzyme-phospholipase A2 released, which acts on membrane phospholipids releasing arachidonic acid and other precursors of PG. They under the action of prostaglandin synthetases are converted into PG, which cause the appearance of uterine contractions. The uterine activity leads to decidual ischemia, which in turn stimulates further release of lysosomal enzymes, after which the PG synthesis cycle enters a stable phase.

As the delivery progresses, there is a constant increase in the blood levels of PGF2a and PGE2, which confirms the thesis that an increase in intrauterine synthesis of PG is the reason for the appearance and strengthening of uterine contractions leading to the successful completion of labor.

The most interesting and modern theory of the development of labor is the theory advanced by Lerat (1978). The author believes that hormonal factors are the main factors in development of labor: maternal (oxytocin, PG), placental (estrogens and progesterone) and fruit hormones of the adrenal cortex and the posterior lobe of the pituitary gland. Hormones of the adrenal cortex change at the level of the placenta the metabolism of steroid hormones (decrease in progesterone production and increase in the level of estrogen). These metabolic shifts, with local action, lead to the appearance of PG in the decidua, the latter have a luteolytic effect, increase the release of oxytocin in the pituitary gland of the woman and increase the tone of the uterus. Isolation of oxytocin by the fetus may cause the onset of labor, which then develops mainly under the influence of the mother's oxytocin.

In modern work Khan, Ishihara, Sullivan, Elder (1992) showed that decidual cells, which were previously isolated from macrophages, after generation give rise to 30 times more PGE2 and PGF2a in culture than in cells before birth. This increase in the level of prostaglandins in culture is noted for 72 hours and is associated with an increase in the number of cyclooxygenase cells from 5 to 95%. At the same time, no changes in the function of macrophages have been detected. The above data show that an increase in the level of GHG from stromal cells is an important source of PG in childbirth.

As is known, the importance of PG of the E2 and F2 series in childbirth has been convincingly demonstrated by a number of researchers, but the tissues of the body, which are the main source of these PGs in labor, have not yet been identified. In particular, the formation of PG by amnion has been studied, and changes in PGE2 in amnion during labor have been determined, but only in recent years it has been revealed that a very small amount of PGE2 is synthesized by amnion and it passes through choriodecid without its metabolism. Thus, the synthesis of PGE2 by the amnion at the onset of labor is unlikely. The relationship between the synthesis of PG decidua and intrauterine infection has been proved. It is known that in terminated pregnancy, decidua contains both types of cells - stromal cells and macrophages. Decidua stroma cells are the main source of PG in human births (decidua macrophages account for 20%) of decidua in term of full term pregnancy. Most of the researchers studied the synthesis of prostaglandins in decidua, without dividing cells into stroma and macrophages. However, further research is needed to elucidate intracellular mechanisms for the synthesis of PG cells by decidua stroma cells. This confirms the thesis that increasing intrauterine synthesis of PG causes the appearance and strengthening of uterine contractions, leading to a favorable end of labor. It is also shown that the cause of a significant increase in the production of PGE and PGF in decidual tissue and human myometrium is oxytocin. Oxytocin, both from the fatal and from the maternal organism, can be a source of increased synthesis of PG. Oxytocin stimulates the production of PG in the pregnant uterus when the uterus is sensitive to oscitocin, while the PGs in turn increase the strength of the oxystocin and cause a reduction in the myometrium and dilatation of the cervix.

trusted-source[1], [2], [3], [4], [5], [6], [7], [8]

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