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.

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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.

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Frequency:
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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.

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.

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TREATMENT @

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.

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.

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MEDICATION @

The most common medication used for treatment of dystocia is oxytocin.
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Drug Category: Oxytocic agents -- Produces rhythmic uterine contractions and can stimulate contraction of the gravid uterus.

Drug Name
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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
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BIBLIOGRAPHY @