Characteristics of childbirth

To clarify the nature of the breach of contractile activity of the uterus in the early stages of its development, along with the study of coordination, strength and frequency, duration and rhythm of uterine contractions, it is also necessary to take into account the disturbances of the tone of the uterus.

When studying the dynamics of cervical dilatation during normal delivery by the method of internal hysterography, Lindgren believed that during the delivery in the uterus there is the same pressure everywhere, since with the sufficient amount of water in the uterine cavity during fights and in pauses between them, the same pressure arises. In addition, when using the Malmstroma registrar, the same pressure was also found during fights in both the uterine cavity and the lower pole of the head. Lindgren in the quantitative recording of the pressure between the fetal head and the uterine wall revealed other pressure ratios that did not correspond to the values of the amniotic pressure.

As is known, the increase in the cesarean section in many countries is due to dystocia in childbirth or the lack of progress in cervical dilatation. In order to reduce the rate of cesarean delivery, these birth attendants are offered active delivery with high doses of oxytocin, but many midwives are very wary of these recommendations. This is due to ignorance of the physiology of cervical dilatation. It was shown that with induced labor without effect, the pressure between the head and the cervix was low, despite adequate intrauterine pressure, and therefore, for the normal course of labor, it is necessary to establish the proper relationship between the pressure between the head, the lower segment and the cervix. However, these authors' conclusions were purely speculative, without sufficient factual data. The main difficulty in interpreting the earlier works of a number of authors is that they measured not so much the force as the pressure between the head and the cervix of the uterus. Studies have shown that active intrauterine pressure fluctuated within 5-121 mm Hg. Art. (an average of 41.75 ± 16.16 mm Hg), and the active force is 0-ISO gwt (average 35 ± 30.59). This work was the first study in which a special catheter in a number of points measured the forces existing between the fetal head and the cervix in labor. The active force developed between the head and the cervix is independent of intrauterine pressure. Therefore, the development of the highest strength between the fetal head and the cervix is a real chance of ending labor through the natural birth canal, even with an adequate level of uterine activity in different parturient women. The process of opening the cervix is the result of a harmonious impact of the three main components:

• isometric regimen of contraction of smooth muscle cells of the shell of the functional parts of the uterus;
• the volume of myometrium deposited in the vascular reservoirs, the decidual envelope and the cervix of the blood;
• the optimal value of resistance to cervical deformity.

The variants of cervical dilatation during urgent labor were studied and their clinical significance was determined. In this case, the advancement of the presenting part of the fetus through the birth canal occurs synchronously with the process of opening the cervix and with the expansion of the opening of the pharynx, the progress of the presenting part through the birth canal is accelerated. Progressive movement of the fetus in the active period of labor is observed after 3 cm of opening of the uterine throat.

Uterus consists of a very large number of muscles, and according to the general laws of physiology, the appointment of muscles in the animal body - to produce work. Therefore, during labor, the uterus musculature in all parts is active and forms peristaltic motions.

Modern research has shown the possibility of two mechanisms of cervical dilatation during childbirth: longitudinal contraction of the uterine walls, causing an increase in intrauterine pressure, and radial tension as the head moves along the cervix.

To date, there has been no method of separate measurement of intrauterine pressure and radial tension. The authors constructed a voltage converter that minimally reacted to the growth of intrauterine pressure. A probe with 4 such transducers was placed between the fetal head and the mother's uterine neck along the long axis of the fetus. At the end of the probe, the intrauterine pressure transducer made it possible to measure amniotic pressure at the same time. Preliminary studies in 20 parturient women confirmed the possibility of radial tension in the expansion of the cervix.

For the recognition of fights during pregnancy, it is characteristic that there is no uniform overall uterine compaction, and occasionally advancing. In addition, the following criterion is true: if the inner pharynx is still being palpated, therefore, if the cervix does not begin to flatten, then the birth has not yet occurred, fights, if they are even sufficiently felt, should refer to labor during pregnancy. The beginning of smoothing of the cervix (from the side of the opening internal pharynx) is the first sign of the onset of labor.

Among the additional clinical criteria, it is recommended to perform an ultrasound scan for 45 minutes to distinguish true births from "false": the presence of fetal breathing with an estimate of cervical maturity by Bishop less than 9 points clearly indicates "false" births. It is believed that "false" births are more often observed with a higher head of the fetus and about 10% of women with a prolonged latent phase can be referred to as "false" births. The pathological contraction (delayed relaxation) of the isthmus is an important cause of late entry of the head into the pelvic cavity and delayed smoothing of the cervix.

Births with abnormal standing of the contraction ring are observed due to localized pathological contraction of the upper or lower sphincter. It is important to take into account the transition of the latent phase into the active phase of childbirth. In uncomplicated births, in primary and maternal females there is the same dynamics of opening of the uterine throat. The discovery of the cervix is itself sufficiently objective to characterize the course of labor. When opened at 5 cm, 90% of parturient women are in the active phase, with the opening of less than 4 cm, 25% of the parturient women are still in the latent phase of labor. It is advisable to diagnose the disturbances of the active phase when opening the uterine pharynx by 5 cm.

Some authors [Johnston, Greer, Kelly, Calder] believe that the level of prostaglandins of the F and E series and their metabolites can be determined by normal birth and pathological. Spontaneous delivery is associated with an increase in metabolites of prostaglandins in the blood plasma in the mother and PGF ₂ is an important stimulant of uterine activity, and its relative deficiency leads to dysfunction of labor. At present, attention has been paid to the role of the pelvic cavity in moving the fetal head during the interpretation of physiological genera. Hydrostatic pressure in the uterine cavity is of particular importance. The forces of contractions of the muscles of the abdominal wall and the walls of the uterus affect the hydrostatic pressure in the cavity of the small pelvis, stimulating the advancement of the fetal head.

In recent years, a number of questions have been clarified as to the relationship between motor function of the uterus and blood flow in the uterus during pregnancy. Increased blood filling of the uterus reduces the activity of the myometrium, and this coincides with the studies of domestic scientists. Amniotomy, according to Brotanek, is always accompanied by a decrease in blood flow, and the increase in the tone of the uterus begins only after the blood flow level stabilizes at a lower level than before the autopsy of the fetal bladder. In the active delivery phase, each contraction of the myometrium is preceded by a decrease in blood flow in the uterus for 30 seconds. With the beginning of the contraction, its level begins to equalize, but again falls sharply as soon as the force of uterine contractions begins to exceed 30 mm Hg. Art. With a peak in the decrease in blood flow at the height (acme) of contraction.

Studying the relationship between contractile activity of the uterus and the blood flow, it is noted that during the contraction the blood flow decreases, and during hypertension of the uterus it decreases to a greater extent. During a severe contraction, the minimum blood flow in the uterus falls on the descending part of the contraction curve. Doctors called this "the phenomenon of slowing the uterine blood flow." The last is 20-40 seconds. In this case, the possible connection of this phenomenon with the development of late decelerations of the type "dip 2" is emphasized.

Our observations on the nature of contractile activity of the uterus according to two-channel internal hysterography show that diastole (the descending part of the uterine contraction curve) with weakness of labor activity is not subject to changes as the uterine throat opens, which can be one of the moments of a violation of uterine self-regulation and thus lead to a decrease in uterine blood flow precisely at the moment of determining the descending part of the contraction curve. It is possible that this may be due to changes in the shape of the uterus itself at the time of the contract and in the pause between contractions, as was shown by echographic studies. It was revealed that in the transverse scanning during the contraction the uterus is round in shape, and in the pause between the contractions it assumes a horizontal ovoid shape. Theoretically, it can be assumed that increasing intrauterine pressure gives the uterus a spherical shape, which is confirmed by this study. In addition, the echography revealed a characteristic swelling of the inferior posterior wall of the uterus (body) towards the sacrum.

It is believed that in the process of evolution in the hemodynamic system of the human uterus, a mechanism of depositing blood into the internal vascular reservoirs of the uterus has appeared, which eventually became the tool of active formation of the magnitude of the hydrodynamic extraovulatory volume expelled from the uterine body cavity into the cylindrical part of the cavity of the lower segment, of this volume back to the passive part of the labor contraction, which determines the biomechanics of opening the cervix in the first stage of labor in humans.

The main parameters of the motor function of the uterus during childbirth. From a brief review of modern data on the contractile activity of the uterus, it can be seen that the same phenomena (parameters) of the motor function of the uterus in different jobs receive a different interpretation. The difference is often can not be considered in the spirit of the sacramental formula: some studies give a true picture of the nature of the contractile activity of the uterus, while others - distorted. This is, obviously, because the processes in the mechanisms of uterine self-regulation have many different, yet unknown sides and faces.

The method of assessing the progress of labor in opening the uterine throat was most widely used. A graphic depiction of the opening of the cervix in labor was introduced in 1954 by EA Friedman. However, it should be recognized that the use of this method does not always give a clear correlation between the dynamics of uterine activity and the opening of the uterine throat. This gave rise to some authors to argue that the slow opening of the uterine pharynx depends, in the main, on a small, and not optimal, uterine activity.

Special computer programs were developed and implemented with the aim of predicting childbirth for hysterographic data, and also for clinical signs. The main difficulty is to determine the most informative indicators with which you can quickly establish the correct diagnosis at the beginning of labor.

Attempts of the mathematical analysis of the most informative signs according to the data of the five-channel external hysterography were made. The considerable unevenness of the qualitative and quantitative indices of the contractile activity of the uterus in the process of the genital act was observed, combined with significant individual variability of the dynamics and duration of the main phases of the generic act, which significantly complicates the generalized partographic and tocophe characteristics of the genera generally. This proves the expediency of practical use of the step-by-step analysis of labor by their phases on the basis of systematic partographic and tomographic monitoring taking into account the state of the cervix and a systematic comparison of the amplitude-time parameters of the uterine cycle with those typical for the normal uncomplicated course of the birth act.

In the foreign literature, the method of evaluating the contractile activity of the uterus in units of Montevideo, where the average value of intrauterine pressure (the amplitude of contraction above the basal line) is multiplied by a multiple of the number of uterine contractions in 10 min., For the purpose of measuring intrauterine pressure in labor.

Also used is the Alexandria unit, which in addition to the Montevideo unit also includes the average duration of reduction per minute.

There is also an "active planimetric unit" - the area under the continuous curve of intrauterine pressure within 10 min, and also the "general planimetric unit" - the area above the active pressure of the curve in 10 min. However, these methods are very laborious and require a lot of time for the analysis of hysterograms.

The total area under the intrauterine pressure curve can be used most rationally, because, according to Miller, the tone of the uterus and the amplitude of the contractions may indicate more fully the degree of progress of the opening of the uterine throat. The uterine activity is measured in torr-minutes (i.e., in mm Hg / min). This method gives a high dependence between the values of uterine activity and the opening of the cervix, which can not be achieved by other methods.

In domestic works there are also attempts to quantitatively analyze hysterograms.

Great importance is attached to the frequency of fights, believing that the more often the rhythm becomes and the more shortened the intervals, the greater the tonus of the uterus between contractions, up to the development of complexes of dis-coordinated abbreviations. It turned out that the tone during the normal delivery varies very slowly, increasing by about 1 mm Hg. Art. Every hour of the generic act. An increase in the tone is always accompanied by more contractions. Doctors suggest that the tone and frequency of contractions are interdependent, and their nature is unified and depends on the degree of excitability of the uterine musculature. It can not be stressed that, according to research, there has been no significant increase in the tone of the uterus without a corresponding increase in contractions. Proceeding from this, they come to the conclusion that out of all the indicators used to assess the contractile activity of the uterus in childbirth, changes in tone in quantitative terms are least demonstrative according to internal hysterography, not to mention external hysterography, and to a lesser extent than the rest indicators - coordination, strength, duration, frequency and rhythm of labor, which are amenable to immediate evaluation. Therefore, the authors doubt the practical expediency of using changes in the tone as the main indicator that determines the various anomalies of labor. Thus, the authors question the usefulness of using those classifications of abnormalities of labor, where the tone of the uterus is based.

The famous German scientist N. Jung in his clinical and experimental studies adheres to the opposite point of view. Our research also confirms it. The author introduced the concept of "tonic and phase double principle of contraction of the uterus." Considering the question of the tonic and phase system of the uterus, the author points out that the contraction is purely tetanic contraction, and the force of contraction is primarily regulated by the frequency of excitations. Studies carried out with the removal of potentials from an individual fiber show that the uterus of the animal and human responds to an increase in the extracellular potassium concentration by decreasing the membrane potential while simultaneously increasing the mechanical frequency and rest tone. If the potential decreases to. Of a certain value, the sodium carrier is inactivated, the muscle reacts only tonic with additional depolarization. On the basis of these results, one can not simply explain the rise in tone caused by oxytocin by a shortened relaxation time as a result of a strong increase in frequency.

As our studies have shown, with the weakness of labor activity, the intensity of metabolic acidosis increases, the total content of nucleic acids, potassium and calcium decreases, along with an increase in oxytocinase activity and inhibition of creatine phosphokinase. The introduction of oxytocin in buffer containing Tris, KCl, CaCl ₂ in certain ratios, normalizes generic activity, as was shown in experimental studies H. Jung. Moreover, the author, in a critical examination of hysterograms, noted that in the clinical setting, after the introduction of the parenteral oxytocin, the tone does not return to the initial tone even when the time interval between contractions is accidentally prolonged at least once. The increase in frequency and tone after giving oxytocin gives a similar picture with that after depolarization of potassium. The dependence is explained for the first time by N. Jung in 1957, depolarizing, i.e., lowering the membrane potential, by the action of oxytocin. The frequency and increase in tone, as well as an increase in excitability, are associated with a lowering of the threshold due to depolarization. This mechanism was confirmed by A. Csapo in 1961 and by other authors.

Important biochemical mechanisms of action of oxytocin on the uterus are increased metabolism of phosphoinositides and inhibition of adenylate cyclase activity. It has been shown that the effect of forskolin (an activator of adenylate cyclase), as well as other substances that increase the level of cyclic adenosine monophosphate in the cell, indicates the involvement of the adenylate cyclase system in the reduction of myometrium, especially in maintaining the tone.

Thus, scientists from the current position of the biochemistry of the uterus confirm earlier observations that, obviously, the adenylate cyclase system is responsible for the tonic component, and phosphoinositide is responsible for the phase component of the human myometrium reduction. Therefore, the management of these processes through the receptors of oxytocin, and also through the influence on intracellular processes of the realization of the phase and tonic components of contraction is very promising for the regulation of labor. Synthesis of analogues of oxytocin blocking or exciting different subtypes of oxytocin receptors will enable to activate or reduce the selectively tonic or phase component of uterine contraction.

This proves the functionally independent principle of tonus in the uterus and found a relationship between the tone and the potential of the membrane.

It is shown that the development of dominant contractile activity in a certain area of the myometrium depends on the intensity of the stimulus, the degree of excitability, and also the conductivity of the myometrium. The existence of centers that cause uterine contractions with their permanent location is subject to criticism in view of:

• absence of any local morphological features;
• a more abundant distribution of nerve fibers in the underlying segments of the uterus;
• known experimental studies, indicating the possibility of the appearance of action potentials in any part of the myometrium.

The so-called "phase (rhythmic) and tonic contraction systems" operate functionally separately from each other, although close functional correlation can be found at normal and at average values of the membrane potential.

The increase in tone, however, can not be explained solely by the secondary high frequency of contractions. In support of this position, Jung provides clinical observations with an accurate analysis of numerous hysterograms with a high tone and a high frequency of fights, with the observation of individual longer pauses between contractions, the tone in these cases not falling further.

These studies show that it is now premature to clinically abandon those classifications where tonus changes are placed as the main indicator determining various abnormalities of labor. There is ample evidence that normal labor can only be observed when there is optimal birth activity with an amplitude of 50-70 mm Hg. Art. And with a contraction frequency of at least 3 cuts in 10 minutes.

Weakness of labor according to the dynamics of intrauterine pressure is characterized by parameters of the amplitude of uterine contractions, equal to 25-30 mm Hg. Art. Or abnormally low frequency of contractions - less than 3 fights in 10 minutes. If the activity of the uterus is less than 100 units. Montevideo, the progression of labor will be slower than normal. In this case, if the contractions of the uterus have an average intensity of 50 mm Hg. Art. And the frequency of bouts is maintained between 4 and 5 contractions in 10 minutes, the duration of the I period will be between 3 and 6 hours.

It is important to note that changes in the acid-base state of fetal blood begin to occur with frequent contractions of the uterus exceeding 5 in 10 minutes, or the basal (residual) tone of the uterus exceeds 12 mm Hg. Art. Leads to a decrease in pH, that is, an increase in uterine activity above optimal contractile activity leads to an increase in the frequency of fetal hypoxia, because uterine contractions are a recurring stress for the fetus in childbirth.

The intensity of contractions increases from 30 mm Hg. Art. In the beginning of childbirth up to 50 mm Hg. Art. At the end of the first stage of labor. The frequency of contractions increases from 3 to 5 cuts in 10 minutes and basal tone of the uterus from 8 to 12 mm Hg. Art. In primiparas, the intensity of uterine contractions is greater than in those who have multiplied.

Domestic clinicians have long noticed the intensification of labor in the position of the parturient woman on her side, respectively, the position of the fetus.

Caldeyro-Barcia (1960) formulated the "position law" when the woman in labor lies on her side (right or left) - the uterine contractions increase with a simultaneous decrease in the frequency of contractions compared to the position of the mother in the back. This leads to practical recommendations - in the presence of so-called tahisistolia (frequent contractions) and hypertension of the uterus, as well as in the presence of uncoordinated uterine contractions in spontaneous labor and a small opening of the uterine throat (by 1 cm), on the one hand, a decrease in basal tone and reduction in the frequency of contractions and an increase in the intensity of uterine contractions. On the other hand, uterine contractions on the side become coordinated, but the mechanism of this action is unknown. The position law is observed in 90% of parturient women with spontaneous labor and in 76% with oxytocin-induced labor. The difference in the average values when the position changes is according to the intensity of the fights - 7.6 mm Hg. Art. And 0.7 cuts in 10 minutes on the frequency of contractions. It is interesting that the differences in the prenatal period and in the period of disclosure were not noted.

Thus, in the presence of frequent bouts, combined with hypertension of the uterus, the woman in labor should be placed on her side. Some scientists, for example Pinto, believe that the mechanical concept of the relationship between uterine activity and cervical dilatation is available only at the end of the second period (the period of exile) and in the succession period, but not in the period of disclosure.

The main indicators of contractile activity of the uterus are tone and excitability. The tone of the uterus can be judged by palpation through the abdominal wall or with a tonometer.

It is noted that the most important feature of contractile activity of the uterus in the normal course of labor is the presence of regular and coordinated uterine contractions, which as the delivery progresses increase in strength and duration and decrease from the bottom to the body and then to the lower segment of the uterus.

[1], [2], [3], [4], [5], [6], [7], [8]