Weakness of labor activity – insufficient contractile activity of the uterus in strength, duration and frequency, due to its hypotonic dysfunction. Pathology is manifested by rare, short and ineffective contractions, slowing down the opening of the cervix and the advancement of the fetus. Disease is diagnosed by observation, cardiotocography, vaginal examination. In the treatment of weakness of labor, labor stimulation is used; according to the indications, a caesarean section is performed.
Weakness of labor activity is one of the forms of violation of the contractile function of the uterus, characterized by low myometrial tone, rare frequency of contractions, weak amplitude of contractions. There is a predominance of the diastole of contractions (relaxation period) over the systole (contraction period), which slows down the opening of the cervix and the progress of the fetus through the birth canal.
In obstetrics and gynecology, weakness of labor activity is one of the frequent complications of childbirth and the most common cause of various pathological conditions of the fetus and mother. Among the total number of births, according to statistics, the weakness of labor activity accounts for about 7% of cases, while the anomaly develops more often in primiparous, less often in the process of the second and subsequent births.
A wide range of causes associated with morphological inferiority of the uterus, insufficiency of hormonal regulation of labor, functional inertia of nervous structures, extragenital diseases, pregnancy pathology, etc. can lead to the development of weakness of labor activity. Weakness of labor activity can occur with uterine pathology (hypoplasia, fibroids, chronic endometritis, adenomyosis, bicornular or saddle uterus), as well as structural failure of the myometrium due to medical intakes, diagnostic curettage, conservative myomectomy and other interventions in the past. Scarring changes that have arisen after radical treatment of cervical erosion in unborn women can also contribute to the weakness of labor.
Often, the reason for the weakness of labor forces is a violation of the balance between factors that cause active labor activity (prostaglandins, estrogens, oxytocin, calcium, mediators, etc.) and inhibiting labor activity (progesterone, magnesium, enzymes that destroy mediators, etc.). Weakness of labor activity often develops in women with vegetative-metabolic disorders – obesity, hypothyroidism, hypofunction of the adrenal cortex, hypothalamic syndrome.
This pathology may be due to the late or young age of the first-time mother; gestosis; premature birth or delayed pregnancy; overgrowth of the uterus with multiple births, large fetus, polyhydramnios; disproportion between the size of the fetus and the pelvis of the woman in labor (narrow pelvis); early discharge of water. Placenta previa, pregnancy in conditions of chronic fetoplacental insufficiency, fetal pathology (hypoxia, anencephaly, etc.) can lead to the development of weakness of labor activity.
In addition, the weakness of labor activity can be aggravated by the asthenization of a woman (overwork, excessive mental and physical exertion, poor nutrition, insufficient sleep); fear of a woman in labor, an uncomfortable environment, inattentive or rude service. The weakness of labor activity is often a direct continuation of the pathological preliminary period of labor.
According to the time of occurrence, there is a primary weakness of labor activity and a secondary one. Primary weakness is considered a situation in which insufficiently active (weak in strength, irregular, short-lived) contractions develop from the very beginning of labor. Secondary weakness is spoken of if there is a weakening of contractions at the end of the 1st or beginning of the 2nd period of labor after the initially normal or violent nature of labor activity.
The types of weakness of labor include segmental and convulsive contractions. Convulsive contractions are characterized by prolonged (more than 2 minutes) contractions of the uterus. With segmental contractions, not the entire uterus is reduced, but its individual segments. Therefore, despite the continuity of segmental contractions, the effect of them is extremely small. The definition of the clinical form of weakness of labor activity allows you to choose a differentiated tactic in relation to the treatment of disorders.
Clinical manifestations of primary weakness of labor activity are: decreased excitability and uterine tone; frequency of contractions – 1-2 within 10 minutes; duration of contractions no more than 15-20 seconds; amplitude (strength) of contractions of the myometrium – 20-25 mm Hg. The period of uterine contraction is short, the period of relaxation is extended by 1.5-2 times. There is no increase in the intensity, amplitude, frequency of contractions over time.
Contractions with primary weakness of labor activity can be regular or irregular, painless or slightly painful. The course of structural changes in the cervix (shortening, smoothing and opening of the cervical canal and uterine pharynx) is slowed down. Weakness of contractile activity of the uterus often accompanies the period of expulsion, as well as the postpartum and early postpartum period, which leads to hypotonic bleeding. The primary weakness of labor activity leads to a prolongation of the duration of labor, fatigue of the woman in labor, untimely outpouring of amniotic fluid, lengthening of the anhydrous interval.
In the case of secondary weakness of labor activity, initially effective contractions weaken, become shorter and less frequent, until complete cessation. This is accompanied by a decrease in the tone and excitability of the uterus. The opening of the uterine pharynx can reach 5-6 cm without further progression; the progress of the fetus through the birth canal stops. The danger of weak labor consists in increasing the risk of ascending infection of the uterus, the development of fetal asphyxia or its intrauterine death. With prolonged standing of the fetal head in the birth canal, birth injuries of the mother (hematomas, vaginal fistulas) may develop.
To determine the nature of labor, a clinical assessment of the effectiveness of contractions, uterine tone, and the dynamics of labor is carried out. During childbirth, monitoring of uterine contractions (current measurement, cardiotocography) is carried out; the frequency, duration, strength of contractions are analyzed and compared with the norm. So, in the active phase of the 1st period, contractions lasting less than 30 seconds are considered weak. and at intervals of more than 5 minutes; for the 2nd period – shorter than 40 seconds.
With the weakness of labor, the opening of the cervix occurs by less than 1 cm per hour. The degree and speed of disclosure are assessed during the vaginal examination, as well as indirectly – by the height of the contractile ring and the advancement of the head. It is said about the weakness of labor activity if the 1st period of labor lasts for primiparous women for more than 12 hours, and for repeat births – for more than 10 hours. The weakness of the labor forces should be differentiated from discoordinated labor activity, since their treatment will be different.
The choice of treatment regimen is based on the causes, the degree of weakness of labor, the period of labor, the assessment of the condition of the fetus and mother. Sometimes, to stimulate the intensity of contractions, it is enough to catheterize the bladder. If the weakness of labor activity is due to polyhydramnios, an amniotomy is performed. If the woman in labor is overworked and there are no indications of hypoxia and fetal asphyxia, the appointment of medication sleep is indicated, with asthenization, it is advisable to create an estrogenic-calcium background.
The main place in the treatment is given to rodostimulating therapy. For this purpose, an intravenous infusion of oxytocin, the introduction of prostenone, dinoprost is performed. If the labor stimulation is ineffective, a caesarean section is performed. When the fetal head is found in the pelvic cavity, they resort to dissection of the perineum (perineotomy, episiotomy) or the imposition of obstetric forceps.
In the process of pregnancy management by an obstetrician-gynecologist, it is necessary to assess risk factors for the development of weakness of labor activity, and when such factors are identified, preventive medication and psychophysical training is required. Weakness of labor activity almost always leads to a deterioration of the fetus (hypoxia, acidosis, brain edema), therefore, simultaneously with labor stimulation, prevention of fetal asphyxia is carried out.