Weakness of labor (hypoactivity, or uterine inertia)

Weakness of labor is a condition in which the intensity, duration and frequency of contractions are insufficient, and therefore the smoothing of the cervix, opening of the cervical canal and the advancement of the fetus, if it corresponds to the size of the pelvis, proceeds at a slow pace.

A distinction is made between primary and secondary weakness of labor. Primary weakness of labor is that which occurs from the very beginning of labor and continues throughout the period of dilation and until the end of labor. Weakness of labor that occurs after a period of prolonged good labor and manifests itself in the characteristic signs indicated above is called secondary.

Weakness of pushing (primary or secondary) is characterized by their insufficiency due to weakness of the abdominal muscles or fatigue. In practical obstetrics, weakness of pushing is classified as secondary weakness of labor.

The incidence of weak labor is approximately 10%. Often, prolonged labor caused by other abnormalities of labor is unreasonably attributed to weakness.

Primary weakness of labor may result from either a deficiency of the impulses that initiate, maintain, and regulate labor or from the inability of the uterus to perceive or respond with sufficient contractions to these impulses.

In the pathogenesis of weak labor, an important role is played by a decrease in the level of estrogen saturation, a violation of the synthesis of prostaglandins, protein (hypoproteinemia), carbohydrate, lipid and mineral metabolism, and a low level of enzymes of the pentose phosphate cycle of carbohydrates.

Among the anomalies of labor, the most studied is weakness of labor.

Currently, the weakness of labor activity tends to increase from 7.09% to 12.21%.

The proportion of primary weakness of labor activity in relation to secondary has changed. It has been revealed that primary weakness of labor activity accounts for 55% of the total number of cases.

A number of authors note a higher frequency of weakness of labor activity in primiparous women compared to multiparous women. E. T. Mikhailenko believes that weakness of labor activity in primiparous women occurs 4.4 times more often than in multiparous women.

The age of the mother also plays an important role in the frequency of occurrence of weak labor.

Back in 1902, V. A. Petrov wrote that it is more common in young primiparous women (16-17 years old) and in women over 25-26 years old. According to modern authors, this pathology is more common at a young age - 20-25 years. Weakness of labor activity is more common in young mothers and in primiparous women over 30 years old. It is significant that impaired uterine contractility is observed in women over 30 years old in labor 4 times more often than at a younger age.

Primary weakness of labor

The clinical picture of labor with primary weakness of labor forces is varied. Contractions can be very rare, but of satisfactory strength; fairly frequent, but weak and short. More favorable are rare and of satisfactory strength contractions, since long pauses contribute to the rest of the uterine muscles. Smoothing of the cervix and opening of the uterine os occur at a slow pace, which is clearly visible when conducting a partogram.

In case of primary weakness of labor activity, the presenting part remains mobile for a long time, or pressed to the entrance to the small pelvis when it corresponds to the size of the pelvis. The duration of labor increases sharply, which leads to fatigue of the woman in labor. Often, there is an untimely discharge of amniotic fluid, and this contributes to the prolongation of the anhydrous interval, infection of the woman in labor and suffering of the fetus.

Long-term motionless standing of the presenting part in one of the planes of the small pelvis, accompanied by compression and anemia of soft tissues, can lead to the subsequent occurrence of urogenital and intestinal-genital fistulas.

In the postpartum period, hypotonic bleeding is often observed as a result of decreased contractility of the uterus, as well as retention of the placenta and its parts in the uterus; after the birth of the placenta, for the same reason, halo- or atonic bleeding is observed. Inflammatory diseases often occur in the postpartum period.

The diagnosis of weak labor activity is established on the basis of:

• insufficient uterine activity;
• slow rate of smoothing of the cervix and dilation of the uterine os;
• prolonged standing of the presenting part at the entrance of the small pelvis and slow advancement in accordance with the size of the pelvis;
• increased duration of labor;
• fatigue of the mother in labor and often intrauterine suffering of the fetus.

The diagnosis of weak labor activity should be made by dynamic observation of the woman in labor for 2-3 hours. With monitoring observation, the diagnosis can be established after 1-2 hours. In differential terms, it is important to exclude a pathological preliminary period, cervical dystopia, discoordinated labor activity, and clinical discrepancy between the size of the pelvis and the fetal head.

Thus, the main clinical manifestation of weak labor is the prolongation of labor. However, to date, there are conflicting data in the literature on the duration of both normal labor and labor complicated by weak labor. In particular, according to research data, the average duration of normal labor is 6 hours, while with weak labor it increases to 24 hours and even 30 hours.

According to the data, the duration of normal labor is 6-12 hours, but in first-time mothers it can be extended to 24 hours.

According to modern authors, the total duration of labor with a physiological course is 16-18 hours for primiparous women and 12-14 hours for multiparous women.

The duration of labor with primary weakness of labor is 33 hours 15 minutes for primiparous women and 20 hours 20 minutes for multiparous women.

The duration of labor with secondary weakness of labor is 36 hours for primiparous women and 24 hours for multiparous women.

T. A. Starostina (1977) proposed a classification of weakness of labor activity depending on the duration of labor. The author distinguishes three degrees of weakness of labor activity: I - up to 19 hours; II - from 19 to 24 hours and III - over 24 hours.

The clinical characteristics of the course of labor are given on the basis of palpation assessment of the contractile activity of the uterus (intensity and duration of contractions, their frequency, duration of the interval between contractions), the dynamics of the opening of the cervix and the movement of the fetus along the birth canal. According to N. S. Baksheev (1972), the duration of an effective contraction, determined by palpation, from the beginning of contraction to the beginning of relaxation of the uterus is 35-60 sec. One contraction should occur no more often than every 3-4 minutes. More frequent and shorter contractions are ineffective.

In primary weakness of labor, contractions are frequent, prolonged, but weak; the opening of the cervix is very slow. According to L. S. Persianov (1975), the most unfavorable contractions are weak, short-term and irregular, up to the complete cessation of contractile activity of the uterus.

An important criterion for the clinical course of labor is the rate of cervical dilation. According to L. S. Persianinov (1964), if 12 hours have passed since the onset of labor for primiparous women and 6 hours for multiparous women and the cervical os has not dilated to three fingers (6 cm), then there is weakness of labor. It is believed that during normal labor, the cervix dilates by 8-10 cm in 10-12 hours of labor, and with weakness of labor, the cervix dilates by 2-4 cm during the same time, rarely by 5 cm.

Fatigue of the uterine muscles, impairment of its motor function with weak labor activity is one of the main causes of various complications of childbirth, the afterbirth and postpartum periods, as well as negative effects on the body of the mother, fetus and newborn. There is a high frequency of untimely discharge of amniotic fluid with weak labor activity from 27.5% to 63.01%. In 24-26% of women in labor, the frequency of surgical interventions increases (obstetric forceps, vacuum extraction of the fetus, cesarean section, fetal-destroying operations).

With weak labor activity, pathological bleeding in the afterbirth and early postpartum periods is observed much more often: over 400 ml in 34.7-50.7% of women in labor. Weak labor activity is one of the causes of postpartum diseases. With an anhydrous interval of up to 6 hours, postpartum diseases occur in 5.84%, 6-12 hours - in 6.82%, 12-20 hours - in 11.96% and more than 20 hours - in 41.4% of cases.

Secondary weakness of labor

Secondary weakness of labor is most often observed at the end of the period of cervical dilation and in the expulsion period. This anomaly of labor occurs in approximately 2.4% of the total number of births.

The causes of secondary weakness of labor are varied. Factors that lead to primary weakness of labor may be the cause of secondary weakness of labor if they are less pronounced and show their negative effect only at the end of the dilation period and in the expulsion period.

Secondary weakness of labor is most often observed as a result of a significant obstacle to delivery in the case of:

• clinically narrow pelvis;
• hydrocephalus;
• incorrect insertion of the head;
• transverse and oblique position of the fetus;
• intractable tissues of the birth canal (immaturity and rigidity of the cervix, its cicatricial changes);
• vaginal stenosis;
• tumors in the pelvis;
• breech presentation;
• severe pain during contractions and pushing;
• untimely rupture of the amniotic sac due to excessive density of the membranes;
• endometritis;
• inept and indiscriminate use of uterotonic drugs, antispasmodics, painkillers and other drugs.

Symptoms of secondary weakness of labor are characterized by an increase in the duration of labor, mainly due to the expulsion period. Contractions, which were initially quite intense, long and rhythmic, become weaker and shorter, and the pauses between them increase. In some cases, contractions practically stop. The movement of the fetus through the birth canal slows down sharply or stops. Labor becomes protracted, leading to fatigue of the mother, which can contribute to the development of endometritis during labor, hypoxia and death of the fetus.

Diagnostics. The diagnosis of secondary weakness of labor activity is based on the clinical picture presented, and objective methods of its registration (hystero- and cardiotocography) in the dynamics of labor are of great help.

To decide on medical tactics, it is necessary to try to establish the cause of secondary weakness.

It is very important to differentiate secondary weakness of labor from clinical discrepancy between the size of the pelvis and the fetal head.

Management of labor in case of secondary labor weakness

The question of medical tactics is decided after establishing the cause of secondary weakness of labor. Thus, in the case of secondary weakness of labor that occurs due to excessive density of the membranes, their immediate opening is indicated. It is very important to differentiate secondary weakness of labor from clinical discrepancy between the size of the pelvis and the fetal head.

The best way to combat secondary weakness of labor in the first stage of labor is to provide rest to the woman in labor (electroanalgesia, GHB); after awakening, monitor the nature of labor for 1-1 % of the hour and, if it is insufficient, labor stimulation with one of the above-mentioned agents (oxytocin, prostaglandin) is indicated. It is necessary to administer antispasmodics and analgesics, and prevent fetal hypoxia. In the expulsion period, with the head standing in the narrow part of the pelvic cavity or at the exit, oxytocin is administered (0.2 ml subcutaneously) or an oxytocin tablet (25 U) is given behind the cheek.

If conservative measures are ineffective, surgical delivery is indicated (application of obstetric forceps, vacuum extractor, extraction of the fetus by the pelvic end, etc.), depending on the existing conditions, without waiting for the appearance of signs of acute fetal hypoxia, since in such cases the operation will be more traumatic for the suffering fetus.

If the advancement of the head, located on the pelvic floor, is delayed due to a rigid or high perineum, a perineotomy or episiotomy should be performed.

In case of secondary weakness of labor activity in combination with other unfavorable factors and the absence of conditions for delivery through the natural birth canal, a cesarean section should be performed. In the presence of infection in women in labor, the method of choice is extraperitoneal cesarean section or cesarean section with temporary delimitation of the abdominal cavity.

In case of signs of developing infection, as well as in case of an anhydrous interval of more than 12 hours, if the end of labor is not expected in the next 1-1 % hours, the use of antibiotics (ampicillin, ampiox, etc.) is indicated.

In order to prevent bleeding in the afterbirth and early postpartum periods, it is necessary to administer uterotonic agents (methylergometrine, oxytocin, prostaglandin).