Background: Dystocia is defined as abnormal or difficult labor, whereas eutocia describes normal labor or childbirth, and oxytocia describes rapid labor. Dystocia itself entails a vast number of influencing factors that include both maternal and fetal entities. The health maintenance and economic benefit of accurately diagnosing dystocia is crucial. It is well known that the cesarean delivery rate for the past 20 years in the US consistently is 50-75% greater than the rate in Europe.
Although simultaneous improvement in perinatal mortality and morbidity rates has been documented, this improvement has not been the result of an increased rate of cesarean deliveries. From an economic standpoint, vaginal delivery is less expensive than an abdominal delivery both for the delivery itself and the hospital stay. This article identifies, discusses, and analyzes maternal and fetal factors relating to dystocia and its management.
Pathophysiology: To characterize a labor as abnormal, a basic understanding of normal labor is necessary. Normal labor starts with regular uterine contractions that are sufficient enough to result in cervical effacement and dilation. Early in labor, uterine contractions are irregular, and cervical effacement and dilation are gradual. The active phase of labor commences when cervical dilation reaches 4 cm and uterine contractions are more powerful. Studies by Friedman from the 1950s were among the first stepping-stones in the understanding of normal labor. His studies established the minimum criteria for dilatation of the cervix during the active phase of 1.2 cm/h for nulliparous women. For parous women, a minimum of 1.5 cm/h of cervical dilatation is accepted as the norm. It is of utmost importance to remember that these rates of cervical dilatation are considered an average and that the active phase of labor does not necessarily start at a specific dilatation.
Dystocia is considered the result of any of the following during labor: (1) abnormalities of expulsive force; (2) abnormalities of presentation, position, or development of the fetus; and (3) abnormalities of the maternal bony pelvis or birth canal. Frequently, combinations of these 3 interact to produce a dysfunctional labor.
Mortality/Morbidity: Dystocia is associated with increased maternal and fetal mortality and morbidity. Treatment for dystocia, which includes cesarean delivery, also is associated with increased maternal mortality and morbidity including damage to other organs, impairment of future fertility, and wound infection. Infant morbidity is minimal and mostly is related to iatrogenic lacerations upon performance of the hysterotomy incision. However, infants delivered through cesarean section are at higher risk for transient tachypnea of newborn and for prematurity.
Race: The incidence of dystocia generally is not associated with any particular race. Shy and colleagues studied the relationship between maternal birth weight, race, and risk for cesarean delivery in nulliparous women. In this population-based cohort study, low and high maternal birth weights were found to exert an intergenerational risk for non-Hispanic white females only in regard to dystocia with subsequent abdominal delivery.
History: Besides complete history, special attention is necessary to determine if a patient is in active labor. Labor is defined as the onset of regular contractions that cause cervical dilatation. The patient must be questioned as to the onset of regular contractions, frequency, intensity, and duration of the contractions. The patient's last cervical examination must be noted to use as a comparison. Past obstetric history and prenatal events should be explored.
The first criterion for diagnosis of an abnormality of the expulsive force is that the patient must be in the active phase of labor, which is defined as a phase of maximal cervical dilatation. With adequate contractions in the active phase, a cervical dilatation rate of at least 1.2 cm/h in nulliparous women and 1.5 cm/h in parous women can be expected. For most women in spontaneous labor, these rates of cervical dilatation are achieved with at least 3-5 contractions in a 10-minute period. If the rate of dilatation is less than expected, the diagnosis of a protraction disorder is made. If evaluation has demonstrated no cervical dilatation in a 2-hour period, the diagnosis is arrest of dilatation.
Before determining a diagnosis of arrest of dilatation, the adequacy of contractions must be evaluated. An intrauterine pressure catheter, which is used to measure the intensity of the contractions, can assess this. Intensity is measured in Montevideo units, which is calculated as the intensity of contractions in millimeters of mercury multiplied by the frequency for a 10-minute period. An adequate contraction pattern is considered one that exceeds 200 Montevideo units in a 10-minute period. If this pattern is present for 2 hours without cervical change, the diagnosis of arrest of dilatation safely can be made.
The effect of anesthesia on the pattern of labor has been reviewed extensively. Recent studies indicate that the use of epidural anesthesia prolongs the active phase of labor as well as the second stage of labor. Despite these findings, studies have noted neither increase in nor correlation of epidural anesthesia and the rate of cesarean delivery. However, a few studies suggest an increased incidence of malpresentation and operative vaginal deliveries.
As labor progresses, the examiner should ascertain if there is asynclitism (the relationship between the anterior and posterior parietal bones and the sagittal suture with the maternal pelvis). If one of the parietal bones precedes the sagittal suture, the head is considered asynclitic. When asynclitism is persistent in either the occiput anterior or the posterior position, use of Kielland forceps can be helpful in correcting the problem. Kielland forceps should only be placed when the fetal head is at a low station (above +2 cm). The sliding lock of the instrument allows accurate cephalic application followed by correction of the asynclitism. Persistent occiput posterior position, leading to a prolonged second stage, also can be corrected by performing a forceps-assisted vaginal delivery with Kielland forceps. Forceps delivery is discussed in more detail in the Surgical Care section. Over time, there are fewer and fewer practitioners comfortable with the use of Kielland forceps.
Any presentation other than occiput increases the probability of dystocia. In either face or brow presentations, dystocia can develop with mentum posterior face presentations. On these presentations, flexion of the head is impeded by compression of the fetal brow under the symphysis pubis.
Another fetal factor that can contribute to dystocia is macrosomia, which is defined as fetal weight of 4500 g or more. Estimated fetal weight should be assessed by Leopold maneuvers in all patients upon presentation to labor and delivery. An estimated fetal weight by ultrasound may be considered in the presence of diabetes mellitus or if maternal obesity makes the estimation of fetal weight difficult. Overall ultrasound predictions of fetal weight fall within 20% of actual fetal weight in the third trimester. Some clinicians opt to proceed with cesarean delivery without a trial of labor in primigravid patients with a fetus believed to be macrosomic. Elective cesarean delivery in this situation is not supported by sound clinical evidence.
Fetuses with anomalies such as hydrocephaly, enlarged abdomen, or neck masses also can present with dysfunctional labors.
The female pelvis can be classified into 4 types based on the shape of the pelvic inlet. Boundaries of the pelvic inlet are (anteriorly) the posterior border of the symphysis pubis and (posteriorly) the sacral promontory and laterally the linea terminalis. The 4 basic types are gynecoid, anthropoid, android, and platypelloid. The gynecoid and anthropoid types have a good prognosis for vaginal delivery while android and platypelloid types have a poor prognosis for vaginal delivery.
Clinical pelvimetry is used to obtain an indirect measure of the obstetrical conjugate, a measurement of the anterior posterior diameter of the pelvic inlet. The average measurement of the obstetrical conjugate is 11-12 cm. An estimate of the obstetrical conjugate is obtained by subtracting 1.5-2 cm from the diagonal conjugate: the distance from the inferior border of the symphysis pubis to the sacral promontory. Another measurement of clinical pelvimetry is the biischial diameter, which is the distance between the ischial tuberosities. This distance is obtained with the patient in the lithotomy position, with a measurement of 8 cm or greater considered being adequate.
In the past, x-ray pelvimetry was routinely performed, but this practice has fallen out of favor given the potential hazard to the fetus. Nevertheless, this practice could be beneficial when considering the mode of delivery for a pregnancy with a fetus in breech presentation.
Medical Care: Management of dystocia depends on the underlying factors of maternal condition and fetal status. When dystocia is the result of inadequate uterine contractions, oxytocin is used. Dystocia as the result of the abnormal fetal position can be corrected and managed by forceps delivery.
Years ago, a policy of active management of labor was adopted in Ireland at the National Maternity Hospital to prevent prolonged labor. In those days, prolonged labor was associated with increased maternal-fetal febrile morbidity and longer hospital stay. A strict management criterion was used as follows:
The program included 1-to-1 nursing by a midwife and a strong prenatal educational program about labor.
The results from Ireland demonstrated that this approach is safe for mother and fetus. It also demonstrated a decrease in operative deliveries, as well as a decrease in the length of labor. The major criticism of the Irish experience on the active management of labor (AMOL) was that the data were not obtained by a randomized clinical trial.
In the US, a few randomized clinical trials (RCTs) have been conducted to study active management of labor. Inherent differences are found among the RCTs in the definitions of onset of active phase and the protocols for active management of labor. Although the results of these RCTs are not as dramatic in the decrease of the cesarean delivery rate, all consistently show a decrease in the duration of labor and a decrease in prolonged labor. Also, all 3 studies consistently demonstrate a decrease in maternal febrile morbidity, which might be a direct effect from shorter labor. More importantly, it must be noted that no RCT demonstrated any increase in the incidence of maternal or neonatal complications.
Surgical Care: Forceps delivery can be performed for transverse arrest of the fetal head. Tucker-McLane or Kielland forceps can be used. An abnormal position such as occiput posterior can be managed with forceps. Vacuum extraction also can be used in some cases with abnormal position. Criteria for use of vacuum extraction should mirror the criteria for use of forceps. Rotation is contraindicated with the vacuum extractor. Any instrument delivery must be performed by a person who is familiar with the instrument and associated criteria.
The most common medication used for treatment of
dystocia is oxytocin.
Drug Category: Oxytocic agents -- Produces rhythmic uterine contractions and can stimulate contraction of the gravid uterus.
|Oxytocin (Pitocin, Syntocinon) -- Nine
amino acid peptide produced in hypothalamus, secreted by posterior pituitary
in pulsatile fashion. Uterine receptors for oxytocin increase during the
weeks before onset of labor with sharpest increase just before labor.
Synthetically produced for pharmacological use. Only IV administration is
acceptable for induction or augmentation of labor. No 1-treatment regimen is
agreed upon due to individual patient variation. Therefore, oxytocin
infusion is titrated to achieve satisfactory uterine contractions. Half-life
is 1-6 min and is cleared from peripheral blood by liver and kidney.
Many clinicians feel comfortable going above the maximum dose if the patient has internal monitoring, the fetal heart tracing is reassuring, and the patient's clinical status requires a higher dose.
|Adult Dose||0.001-0.002 U/min IV; increase by 0.001-0.002 U q15-30min until contraction pattern established; maximum 20 mU/min|
|Pediatric Dose||Not established|
|Contraindications||Documented hypersensitivity; unfavorable fetal positions, and a contracting uterus with hypertonic or hyperactive patterns; nonreassuring fetal status and remote from delivery; labor where vaginal delivery should be avoided such as invasive cervical carcinoma, cord presentation or prolapse, active herpes genitalis, total placenta previa, and vasa previa|
|Interactions||Pressor effect of sympathomimetics may increase when used concomitantly with oxytocic drugs, causing postpartum hypertension|
|Pregnancy||X - Contraindicated in pregnancy|
|Precautions||A uterus that is overstimulated can be hazardous to mother and fetus; hypertonic contractions can occur in a patient whose uterus is hypersensitive to oxytocin regardless of whether it was given appropriately; oxytocin has intrinsic antidiuretic effect that can cause water intoxication when administered by continuous infusion and patient is receiving fluids by mouth|