Characteristics of physiological childbirth

Childbirth is a complex physiological process during which the contents of the uterus (the fetus, amniotic fluid, placenta and fetal membranes) are expelled. The clinical course of this process is characterized by an increase in the frequency, strength and duration of uterine contractions, progressive smoothing and opening of the cervix and the movement of the fetus along the birth canal. Some doctors believe that the following criterion is correct: if the internal os is still palpable, then labor has not yet begun, contractions, even if they are felt quite strongly, should be considered pregnancy contractions. The beginning of smoothing of the cervix (from the side of the opening internal os) is the first sign of the onset of labor.

The beginning of labor is considered to be regular labor activity, when contractions are repeated every 10-15 minutes, i.e. with the correct periodicity, and without stopping, lead to labor.

The entire labor cycle is usually divided into 3 periods:

1. Opening period.
2. Period of exile.
3. The period of birth of the placenta.

The birth canal consists mainly of two parts: the soft birth tube and the bony pelvis.

E. Friedman gave a graphical representation of labor (partogram). These data are most thoroughly displayed in his monograph "Childbirth: clinical assessment and management" (1978). In the methodological recommendations "Anomalies of labor activity". It is considered appropriate to distinguish the latent and active phases in the first period of labor.

The latent phase is the interval (preparatory period according to Friedman) from the beginning of regular contractions until the appearance of structural changes in the cervix and the opening of the uterine os by 4 cm). The duration of the latent phase in primiparous women is approximately 6% h, and in multiparous women - 5 h. The duration of the latent phase depends on the condition of the cervix, parity, the influence of pharmacological agents and does not depend on the weight of the fetus.

Following the latent phase, the active phase of labor begins, which is characterized by the rapid opening of the cervical os (from 4 to 10 cm).

In the active phase of labor, the following are distinguished: the initial acceleration phase, the rapid (maximum) risephase, and the deceleration phase.

The rise of the partogram curve indicates the effectiveness of labor: the steeper the rise, the more effective the labor. The slowing phase is explained by the cervix moving behind the head at the end of the first stage of labor.

The normal rate of advancement of the fetal head when the cervix is dilated to 8-9 cm for primiparous women is 1 cm/h, for multiparous women - 2 cm/h. The rate of descent of the head depends on the effectiveness of the expulsive forces.

For dynamic assessment of cervical dilation during labor, it is advisable to use a partogram (a graphical method for assessing the rate of cervical dilation during labor). The rate of cervical dilation in the latent phase is 0.35 cm/h, in the active phase - 1.5-2 cm/h in primiparous women and 2-2.5 cm/h in multiparous women. The rate of cervical dilation depends on the contractility of the myometrium, the resistance of the cervix and a combination of these factors. Dilation of the cervical os from 8 to 10 cm (slowing phase) occurs at a slower rate - 1-1.5 cm/h. The lower limit of the normal rate of dilation of the cervical os in the active phase in primiparous women is 1.2 cm/h, and in multiparous women - 1.5 cm/h.

At present, a shortening of the duration of labor is observed in comparison with the figures given earlier. This is explained by many factors. The average duration of labor for first-time mothers is 11-12 hours, for repeat mothers - 7-8 hours.

It is necessary to distinguish between precipitate and rapid labor, which are classified as pathological, and according to V. A. Strukov - as physiological. Precipitate labor is labor that lasts less than 4 hours in primiparous women, and less than 2 hours in multiparous women. Rapid labor is considered to be labor with a total duration of 6 to 4 hours in primiparous women, and 4 to 2 hours in multiparous women.

The onset of labor is considered to be regular, painful contractions alternating every 3-5 minutes and leading to structural changes in the cervix. The authors determined the duration of labor in primiparous and multiparous women (total number of observations - 6991 women in labor) with and without epidural analgesia on a large clinical sample. The total duration of labor without anesthesia in primiparous women was 8.1 ± 4.3 hours (maximum - 16.6 hours), and in multiparous women - 5.7 ± 3.4 hours (maximum - 12.5 hours). The second stage of labor was 54 + 39 minutes (maximum - 132 minutes) and 19 ± 21 minutes (maximum - 61.0 minutes), respectively.

When using epidural analgesia, the duration of labor was, respectively, 10.2 ± 4.4 hours (maximum - 19.0 hours) and 7.4 ± 3.8 hours (maximum - 14.9 hours) and the second stage - 79 ± 53 minutes (185 minutes) and 45 ± 43 minutes (131 minutes).

In February 1988, the Committee on Obstetrics and the Use of Obstetric Forceps, taking into account cardiotocography data, recommended not to exceed the duration of the second stage of labor for more than 2 hours, the so-called "2-hour rule". Research by E. Friedman (1978) also showed that the second stage of labor lasting 2 hours is observed in 95% of women in labor. In multiparous women, the duration of the second stage of labor over 2 hours leads to an increase in perinatal mortality. In this regard, obstetric forceps or a vacuum extractor are used when the second stage of labor exceeds 2 hours. The authors are not supporters of this rule when there is no progress in the advancement of the head along the birth canal and there is no fetal distress according to cardiotocography data. Epidural analgesia significantly increases the overall duration of labor in both primiparous and multiparous women. The first stage of labor is extended by an average of 2 hours and the second stage by 20-30 minutes, which is consistent with the data of De Vore, Eisler (1987).

Nesheim (1988), when studying the duration of labor in 9,703 women in labor, showed that the total duration of labor in primiparous women was 8.2 hours (4.0-15.0) and in multiparous women - 5.3 hours (2.5-10.8 hours). The duration of induced labor was 6.3 (3.1-12.4 hours) and 3.9 (1.8-8.1 hours), respectively, i.e., on average, it decreased by 2 hours and 1.5 hours, respectively, while the total duration of normal labor in primiparous women was 3 hours longer than in multiparous women.

It is important to emphasize that the duration of labor has a positive correlation with the fetal weight, the duration of pregnancy, the pregnant woman's weight during pregnancy, and the woman's weight before pregnancy. A negative correlation with the mother's height was found. In addition, an increase in weight by every additional 100 g prolongs labor by 3 minutes, an increase in the mother's height by 10 cm shortens labor by 36 minutes, each week of pregnancy prolongs labor by 1 minute, each kilogram of body weight prolongs labor by 2 minutes, and each kilogram of body weight before pregnancy - by 1 minute.

The duration of labor with anterior occipital presentation in primiparous women was 8.2 (4.0-15.0 h) and 5.3 (2.5-10.8 h) in multiparous women. With posterior occipital presentation, the corresponding figures were 9.5 (5.1-17.2 h) and 5.9 (2.9-11.4 h). A number of factors may play a role in the passage of the fetus through the birth canal (fetal weight and posterior occipital presentation), especially in primiparous women; in multiparous women, they are of little importance. With extension presentations of the head (anterior cephalic, frontal, facial), the duration of labor was 10.0 (4.0-16.2 h) and 5.7 (3.3-12.0 h) in primiparous and multiparous women, respectively; 10.8 (4.9-19.1 h) and 4.3 (3.0-8.1 h); 10.8 (4.0-19.1 h) and 4.4 (3.0-8.1 h). Breech presentations do not prolong labor and are 8.0 (3.8-13.9 h) and 5.8 (2.7-10.8 h), respectively.

A number of modern studies have studied the duration of the second stage of labor and the factors influencing its duration. It is significant that earlier studies of this problem have been significantly corrected in modern studies. Piper et al. (1991) showed that epidural analgesia affects the duration of the second stage and is 48.5 min, and without analgesia - 27.0 min. Parity also has an effect: 0-52.6 min, 1-24.6 min, 2-22.7 min and 3-13.5 min. The duration of the active phase of labor also affects the duration of the second stage - less than 1.54 hours - 26 min; 1.5-2.9 hours - 33.8 min; 3.0-5.4 hours -41.7 min; more than 5.4 hours - 49.3 min. Weight gain during pregnancy also has an effect: less than 10 kg - 34.3 min; 10-20 kg - 38.9 min; more than 20 kg - 45.6 min. Newborn weight: less than 2500 g - 22.3 min; 2500-2999 g - 35.2 min; 3000-3999 g - 38.9 min; more than 4000 g - 41.2 min.

Paterson, Saunders, Wadsworth (1992) studied in detail the effect of epidural analgesia on the duration of the second stage in comparison with women in labor without epidural analgesia on a large clinical sample (25,069 women in labor). It was found that in primiparous women without pain relief, the duration of the second stage was 58 (46) min, with pain relief - 97 (68) min. The difference was 39 min (37-41 min). In multiparous women, the corresponding figures were 54 (55) and 19 (21) min. The difference in the duration of the second stage was 35 min (33-37 min). Taking into account parity, the duration of the second stage was as follows (with epidural analgesia): 0-82 (45-134 min); 1 - 36 (20-77 min); 2-25 (14-60 min); 3 - 23 (12-53 min); 4 or more births - 9-30 min. Without epidural analgesia, respectively: 45 (27-76 min); 15 (10-25 min); 11 (7-20 min); 10 (5-16 min); 10 (5-15 min).

An important issue is also the determination of the time intervals of the second period and its relationship with neonatal and maternal morbidity. This issue is the subject of a study by English authors based on an analysis of materials from 17 clinics and covering 36,727 births in the region in 1988. A detailed analysis was conducted on 25,069 pregnant women and women in labor with a pregnancy period of at least 37 weeks. It was found that the duration of the second period of labor is significantly associated with the risk of obstetric hemorrhage and infection in the mother, and a similar risk is observed in operative deliveries and with a fetal weight over 4000 g. At the same time, fever during labor gives more infectious complications in the postpartum period than the duration of the second period of labor itself. It is very important to note that the duration of the second period is not associated with low Apgar scores or with the use of special care for newborns. The outstanding obstetrician of the XIX century Dennan (1817) recommended a 6-hour duration of the second stage of labor, before the use of obstetric forceps. Harper (1859) recommended more active management of labor. De Lee (1920) suggested prophylactic episiotomy and the use of obstetric forceps to prevent fetal damage. Hellman, Prystowsky (1952) were among the first to point out the increase in mortality in newborns, obstetric hemorrhage and postpartum infection in the mother with a duration of the second stage of labor over 2 hours. In addition, Butler, Bonham (1963), Pearson, Davies (1974) noted the appearance of acidosis in the fetus with a duration of the second stage of labor over 2 hours.

Over the last 10-15 years, these provisions on the risk to the mother and fetus of the second stage of labor have been revised. Thus, Cohen (1977) studied over 4,000 women and found no increase in perinatal mortality or low Apgar scores for newborns with a duration of the second stage of labor of up to 3 hours, and epidural analgesia, despite prolongation of the second stage, does not have an adverse effect on pH in the fetus, and if the position of the mother in labor on her back is avoided, acidosis in the fetus can be prevented.

The authors make an important conclusion that the duration of the second period up to 3 hours does not pose any risk to the fetus.

Thus, on the one hand, the management of labor with reflection on a graph (partogram) allows us to identify the limits of alertness and take timely action. The graphical analysis of labor activity proposed in 1954 by E. A. Friedman reflects the dependence of the opening of the cervix and the advancement of the fetal head on the duration of labor, allowing us to identify possible deviations from the norm. These include:

• prolongation of the latent phase;
• delay in the active phase of cervical dilation;
• delay in head lowering;
• prolongation of the phase of delayed dilation of the uterine os;
• stopping the process of opening the cervical os;
• delay in the advancement of the head and its stop;
• rapid dilation of the cervix;
• rapid advancement of the head.

On the other hand, there are contradictory opinions about the effect of the position of the mother during labor on the condition of the fetus. Mizuta studied the effect of the position of the mother during labor (sitting or lying on her back) on the condition of the fetus. The condition of the fetus, and then the newborn, was assessed based on the analysis of the heart rate, duration of labor, Apgar score data, umbilical cord blood acid-base balance, umbilical cord blood catecholamine levels, and the newborn's heart rate. It was found that primiparous women had significantly less frequent use of fetal vacuum extraction and neonatal depression in the sitting position. In multiparous women, the blood gas composition of the umbilical cord arteries was significantly better in the lying position.

An analysis of the presented data shows that none of the positions of the woman in labor can be considered more favorable in comparison with others.

The clinical course and contractile activity of the uterus during normal labor have been studied. One of the most important indicators of the course of labor is the duration of the labor act by periods and the total duration of labor. It is currently believed that the duration of normal labor is 12-14 hours for primiparous women and 7-8 hours for multiparous women.

According to our study, the total duration of labor in primiparous women was 10.86 ± 21.4 min. On average, in 37% of cases, it is preceded by a normal preliminary period lasting 10.45 ± 1.77 min. The duration of the first stage of labor is 10.32+ 1.77 min, the second stage - 23.8 + 0.69 min, the third stage - 8.7 ± 1.09 min.

The total duration of labor in multiparous women is 7 hours 18 minutes ± 28.0 minutes. In 32% of cases, it is preceded by a normal preliminary period lasting 8.2 ± 1.60 minutes. The duration of the first stage of labor is 6 hours 53 minutes ± 28.2 minutes, the second stage - 16.9 + 0.78 minutes, and the third stage - 8.1 ± 0.94 minutes.

Another important indicator of the clinical course of labor is the rate of cervical dilation.

In the first stage of labor, the rate of cervical dilation has the following picture. The rate of cervical dilation at the beginning of labor until the cervical os opens to 2.5 cm is 0.35 ± 0.20 cm/h (latent phase of labor); with dilation from 2.5 to 8.5 cm - 5.5 ± 0.16 cm/h in multiparous women and 3.0 + 0.08 cm/h in primiparous women (active phase of labor); with dilation from 8.5 to 10 cm, the slowing phase of labor occurs.

Currently, the dynamics and rate of cervical dilation are somewhat different, which is due to the use of various medications that regulate labor (antispasmodics, beta-adrenergic agonists, etc.). Thus, in primiparous women, the rate of cervical dilation from the onset of labor to 4 cm of cervical dilation is 0.78 cm/h, in the period from 4 to 7 cm - 1.5 cm/h, and from 7 to 10 cm - 2.1 cm/h. In multiparous women, respectively: 0.82 cm/h, 2.7 cm/h, 3.4 cm/h.

Contractile activity of the uterus during normal labor has the following features. The frequency of contractions does not change significantly throughout labor and is 4.35 ± 1.15 contractions per 10 min with a shortened cervix, and by the end of labor with an opening of the cervix of 8-10 cm - 3.90 ± 0.04 contractions per 10 min. Confidence intervals are within the range from 2.05-4-6.65 to 3.82-4-3.98 contractions per 10 min.

As labor progresses, the phenomenon of a “triple descending gradient” is observed, which is maintained during normal labor with a dilation of the cervix from 2 to 10 cm in 100%, and with a shortened cervix in 33%.

The time indices of uterine contraction activity (duration of uterine contraction and relaxation, duration of contraction, intervals between contractions, uterine cycle) increase as labor progresses and decrease from the fundus to the body and then to the lower segment of the uterus, with the exception of the interval between contractions, which increases from the fundus to the lower segment. The duration of uterine contraction is less than the duration of relaxation.

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