Dystocia

INTRODUCTION

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.

Frequency:
　

• In the US: In the US, 20-25% of deliveries are by cesarean, and dystocia accounts for 30% of all cesarean deliveries. The diagnosis of dystocia is especially common in nulliparous women and constitutes the single largest indication for primary cesarean delivery. Previous cesarean delivery is the second most common indication for cesarean delivery, followed with fetal distress in 14% of primary cesarean deliveries.

• Internationally: Since the diagnosis of the dystocia is subjective, it is not possible to know the exact frequency in most parts of the world.

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.

CLINICAL

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.

Physical:

• A careful and thorough physical examination must be performed. The examination must include a complete abdominal examination with Leopold maneuvers in order to ascertain presentation and estimate the fetal weight. Clinical estimation of the fetal weight may not be very accurate, especially at higher birth range. This also is the case with ultrasound estimation of fetal weight. One must take note that the margin of error increases with gestational age and weight, especially for larger fetuses (more than 4-4.5 kg).

• The pelvic examination focuses on more than determination of cervical dilatation, effacement, and station. It provides an excellent opportunity to assess the patient's pelvis and perform clinical pelvimetry. Finally, fetal presentation and position must be assessed. It appears to be a common practice to evaluate position once cervical dilatation is advanced or completed, but it is beneficial to know fetal position as early as possible in that fetal position can be a major contributor to dystocia.

• The examiner, preferably the same one each time, should perform a careful cervical examination every 2 hours once the patient is in active labor (certain clinical situations may require modification of this time interval). All of the above named factors (ie, cervical dilatation, effacement, station, position, presentation) should be reevaluated during each examination. Diagnosis of dystocia should be made in a prompt manner so that an attempt to correct the dysfunction can be made without jeopardizing mother or fetus.

Causes:

• Abnormalities of expulsive forces

  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.

WORKUP

Imaging Studies:
　

• X-ray pelvimetry is rarely done in the US, mainly due to the concerns regarding potential hazards and poor predictability. Recently, Thurnau and colleagues suggested a fetal-pelvic index measurement employing ultrasound and x-ray to predict fetal-pelvic disproportion. Maternal pelvic diameters are measured by x-ray and fetal head measurements are measured through ultrasound. Transverse and anteroposterior diameter of the pelvic inlet and midpelvis are measured, then inlet and midpelvic circumferences are calculated. The same is done regarding the fetus, and head and abdominal circumferences are measured. The difference between fetal and maternal circumferences is calculated. The sum of the 2 most positive fetal-pelvic circumference differences is calculated as the Fetal-Pelvic Index (FPI).

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.

• Outlet forceps delivery: The scalp is visible at the introitus without separating labia; the fetal skull has reached the pelvic floor; sagittal suture is anteroposterior, right or left occiput anterior, or posterior; and rotation is less than 45 degrees.

• Low forceps delivery: The fetal head is at greater than +2 station and rotation is greater than 45 degrees.

• Midforceps delivery: The head is above +2 cm, but engaged.

• High forceps delivery is no longer practiced.

MEDICATION

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.

FOLLOW-UP

Complications:
　

• The complications of labor dystocia are more a consequence of the dystocia itself rather than the treatment.

• A labor pattern that is protracted increases the risk of chorioamnionitis and therefore neonatal infection. Given that most laboring patients have either spontaneous or artificial rupture of membranes, the fetus could be at increased risk of infection if the labor time is prolonged. Also, patients with poor progress during labor generally are submitted to multiple vaginal examinations, thus increasing the risk of chorioamniotis.

• Another major complication of labor dystocia is the increased probability of undergoing an abdominal delivery, which carries all of the inherent risks of major abdominal surgery. Among the risks of cesarean section are blood loss, damage to viscera, infection, wound separation, urinary retention, hernia formation, and anesthesia-related complications.

• The risk of shoulder dystocia should be a primary concern for patients with macrosomia and/or diabetes. If true cephalopelvic disproportion is the working diagnosis, an abdominal delivery might be in the best interest of patient and fetus to avoid shoulder dystocia and brachial plexus injury. The diagnosis of true cephalopelvic disproportion is not always obvious except in cases of severe congenital abnormalities or patients who have sustained major trauma to the bony pelvis. Always perform a careful clinical evaluation prior to opting for a cesarean section.

MISCELLANEOUS

Medical/Legal Pitfalls:
　

• Diagnosis of labor dystocia can be difficult, complex, and time-consuming. The approach to the laboring patient is to perform a through sequential manner addressing individually each of the contributing factors of dystocia. Identify contributing factors in a prompt manner and attempt correction of the problem. The principles of active management of labor can be applied safely to the laboring patient in an attempt to decrease the incidence of prolonged labor and cesarean delivery rate.

• The medicolegal aspects of the complications, either neonatal or maternal, are enormous. This is why it is so important to perform a careful, methodical, and comprehensive evaluation of every laboring patient.

Special Concerns:
　

• The patient is in latent phase of labor, which is defined as the period between the onset of labor and a point at which a change in the slope of cervical dilatation is noted. Differentiating between active labor and latent phase of labor can be difficult and most often is identified in retrospect. Careful attention to the course of labor must be taken in that the management of active labor and the treatment of prolonged latent phase are quite different. Overall, the management of prolonged latent phase is either oxytocin augmentation or rest. When rest is chosen with utilization of strong sedatives, the following results can be anticipated:

• Patient enters a labor pattern (85%)

• Contractions cease and therefore the patient has false labor (10%)

• The abnormal latent phase continues, and the patient requires oxytocin stimulation (5%)

• The patient has painful uterine contractions because of placenta abruption and not because of labor.

• Chorioamnionitis can cause contractions without progressive labor. Treatment entails an antibiotic regimen.