8.Dystocia

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Abnormal Labor/Dystocia

Dystocia (antonym eutocia; Greek: tokos "childbirth") is an abnormal or

difficult childbirth or labour. Approximately one fifth of human labours have

dystocia. Dystocia may arise due to incoordinate uterine activity, abnormal

fetal lie or presentation, absolute or relative cephalopelvic disproportion, or

(rarely) a massive fetal tumor such as a sacrococcygeal teratoma. Oxytocin

is commonly used to treat incoordinate uterine activity, but pregnancies

complicated by dystocia often end with assisted deliveries, including forceps,

ventouse or, commonly, caesarean section. Recognized complications of

dystocia include fetal death, respiratory depression, hypoxic ischaemic

encephalopathy (HIE), and brachial nerve damage. A prolonged interval

between pregnancies, primigravid birth, and multiple birth have also been

associated with increased risk for labor dystocia.

To define abnormal labor, a definition of normal labor must be understood

and accepted. Normal labor is defined as uterine contractions that result in

progressive dilation and effacement of the cervix. By following thousands of

labors resulting in uncomplicated vaginal deliveries, time limits and progress

milestones have been identified that define normal labor. Failure to meet

these milestones defines abnormal labor, which suggests an increased risk

of an unfavorable outcome. Thus, abnormal labor alerts the obstetrician to

consider alternative methods for a successful delivery that minimize risks to

both the mother and the infant.

Dystocia of labor is defined as difficult labor or abnormally slow progress of

labor. Other terms that are often used interchangeably with dystocia aredysfunctional labor, failure to progress (lack of progressive cervical dilatation

or lack of descent), and cephalopelvic disproportion (CPD).

Friedman's original research in 1955 defined 3 stages of labor.

The first stage starts with uterine contractions leading to complete

cervical dilation and is divided into latent and active phases. In the

latent phase, irregular uterine contractions occur with slow and

gradual cervical effacement and dilation. The active phase is

demonstrated by an increased rate of cervical dilation and fetal

Total 2 hrs

Intro-

30 mins

Assessment

50 mins

Nursing

care

40 mins

Lecture,

case study,

discussion


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descent. The active phase usually starts at 3-4 cm cervical dilation

and is subdivided into the acceleration, maximum slope, and

deceleration phases. The second stage of labor is defined as complete dilation of the

cervix to the delivery of the infant.

The third stage of labor involves delivery of the placenta.

See images below for the normal labor curves of both nulliparas and

multiparas. The following table shows abnormal labor indicators.

Table. Abnormal Labor Indicators

Indication Nullipara Multipara

Prolonged latent phase >20 h >14 h

Average second stage 50 min 20 min

Prolonged second stage without (with)

epidural

>2 h (>3 h) >1 h (>2 h)

Protracted dilation < 1.2 cm/h < 1.5 cm/h

Protracted descent < 1 cm/h < 2 cm/h

Arrest of dilation* >2 h >2 h

Arrest of descent* >2 h >1 h

Prolonged third stage >30 min >30 min

*Adequate contractions >200 Montevideo units [MVU] per 10 minutes for 2

hours. (Please refer to the Pathophysiology for information regarding

adequate contractions.)

Abnormal labor constitutes any findings that fall outside the accepted normal

labor curve. However, the authors hesitate to apply the diagnosis of

abnormal labor during the latent phase because it is easy to confuse

prodromal contractions for latent labor. In addition, the original labor curve,

as defined by Friedman, may not be completely applicable today.

First stage of labor

Latent phase: Definitions for prolonged latent phase are outlined in the table


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above. Diagnosis of abnormal labor during the latent phase is uncommon

and likely an incorrect diagnosis.

Active phase: Around the time uterine contractions cause the cervix to

become 3-4 cm dilated, the patient usually enters the active phase of the

first stage of labor. Abnormalities of cervical dilation (protracted dilation and

arrest of dilation) as well as descent abnormalities (protracted descent and

arrest of descent) are outlined in the table above.

In general, abnormal labor is the result of problems with one of the 3 P' s.

Passenger (infant size, fetal presentation [occiput anterior, posterior,

or transverse])

Pelvis or passage (size, shape, and adequacy of the pelvis)

Power (uterine contractility)

Pathophysiology

A prolonged latent phase may result from oversedation or from entering

labor early with a thickened or uneffaced cervix. It may be misdiagnosed inthe face of frequent prodromal contractions. Protraction of active labor is

more easily diagnosed and is dependent upon the 3 P' s.

The first P, the passenger, may produce abnormal labor because of the

infant's size (eg, macrosomia) or from malpresentation.

The second P, the pelvis, can cause abnormal labor because its contours

may be too small or narrow to allow passage of the infant. Both the

passenger and pelvis cause abnormal labor by a mechanical obstruction,

referred to as mechanical dystocia.

With the third P, the power component, the frequency of uterine contraction

may be adequate, but the intensity may be inadequate. Disruption of

communication between adjacent segments of the uterus may also exist,

resulting from surgical scarring, fibroids, or other conduction disruption.

Whatever the cause, the contraction pattern fails to result in cervical

effacement and dilation. This is called functional dystocia. Uterine contractileforce can be quantified by the use of an intra-uterine pressure catheter. Use


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of this device allows for direct measurement and calculation of uterine

contractility per each contraction and is reported in Montevideo units

(MVUs). For uterine contractile force to be considered adequate, the forceproduced must exceed 200 MVUs during a 10-minute contraction period.

Arrest disorders cannot be properly diagnosed until the patient is in the

active phase and had no cervical change for 2 or more hours with the

contraction pattern exceeding 200 MVUs. Uterine contractions must be

considered adequate to correctly diagnose arrest of dilation.

Mortality/Morbidity

Both maternal and fetal mortality and morbidity rates increase with abnormal

labor. This is probably an effect-effect relationship rather than a cause-effect

relationship. Nonetheless, identification of abnormal labor and initiation of

appropriate actions to reduce the risks are matters of some urgency.

Nursing assessment

History

Evaluate every pregnant patient who presents with contractions in

the labor and delivery unit.

Any patient in labor is at risk for abnormal labor regardless of the

number of previous pregnancies or the seemingly adequate

dimensions of the pelvis.

Plot the progress of any patient in labor, and evaluate it on a labor

curve (see images below).

Physical

Upon admission to the labor and delivery unit, determine and

document clinical findings.

o Clinical pelvimetry, which is best performed at the first

prenatal care visit, is important in order to assess the pelvic

type (eg, android, gynecoid, platypelloid, anthropoid).

o Evaluate the position of the fetal head in early labor becausecaput and moulding complicate correct assessment as labor


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progresses.

o Establish and document an estimated fetal weight.

o Monitor fetal heart rate and uterine contraction patterns toassess fetal well-being and adequacy of labor.

o Perform a cervical examination to determine whether the

patient is in the latent or active phase of labor.

Addressing these issues allows for an assessment of the current

phase of labor and anticipation of whether abnormal labor from any

of the 3 P' s may be encountered.

Causes

Prolonged latent phase: The latent phase of labor is defined as the

period of time starting with the onset of regular uterine contractions

and ending with the onset of the active phase (usually 3-4 cm

cervical dilation).

o A prolonged latent phase is defined as exceeding 20 hours in

patients who are nulliparas or 14 hours in patients who are

multiparas.

o The most common reason for prolonged latent phase is

entering labor without substantial cervical effacement.

Power: Power is defined as uterine contractility multiplied by the

frequency of contractions.

o Montevideo units (MVUs) refer to the strength of contractions

in millimeters of mercury multiplied by the frequency per 10

minutes as measured by intrauterine pressure transducer.

o The uterine contraction pattern should repeat every 2-3

minutes.o The uterine contractile force produced must exceed 200

MVUs/10 min for active labor to be considered adequate. For

example, 3 contractions in 10 minutes that each reach a

peak of 60 mm Hg are 60 X 3 = 180 MVUs.

o An arrest disorder of labor cannot be diagnosed until the

patient is in the active phase and the contraction pattern

exceeds 200 MVUs for 2 or more hours with no cervical

change. Extending the minimum period of oxytocin

augmentation for active-phase arrest from 2 up to 4 hours


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may be considered as long as fetal reassurance is noted with

fetal heart rate monitoring.

Pelvis or the size of the passageway inhibiting deliveryo The shape of the bony pelvis (eg, anthropoid or platypelloid)

can result in abnormal labor.

o A patient who is extremely short or obese, or who has had

prior severe trauma to the bony pelvis, may also be at

increased risk of abnormal labor.

Abnormal labor could also be secondary to the passenger, the size

of the infant, and/or the presentation of the infant.

o In addition to problems caused by the differential in size

between the fetal head and the maternal bony pelvis, the

fetal presentation may include asynclitism or head extension.

Asynclitism is malposition of the fetal head within the pelvis,

which compromises the narrowest diameter through the

pelvis.

o Fetal macrosomia and other anomalies (including

hydrocephalus, encephalocele, fetal goiter, cystic hygroma,

hydrops, or any other abnormality that increases the size of

the infant) are likely to cause deviation from the normal labor

curve.

Other factors include either a low-dose epidural or combined

spinal-epidural anesthetics that minimize motor block and may

contribute to a prolonged second stage. These have also been

associated with an increase in oxytocin use and operative vaginal

delivery. However, use of epidural for analgesia during labor does

not result in a statistically significant increase in cesarean delivery.

Intravenous oversedation has also been implicated as prolonginglabor in both the latent and active phases.

An 11-year review by Zuo et al found significant correlation of

reactive, infectious, atypical, and dysplastic cytologic changes

during pregnancy with abnormal placental findings; all but dysplastic

cytologic changes had significant association with preterm birth. The

study also found that the presence of high-risk human papillomavirus

(HPV) DNA was associated with placental abnormalities and preterm

birth. This suggests that cervical infection of HPV is a risk factor forpreterm birth; thus, cervical cytology is an effective tool for screening


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women.

Differentials

Abruptio Placentae

Amnionitis

Other Tests

The simplest test used to evaluate abnormal labor is to plot the

patient's labor progress (cervical dilation vs duration in hours) on a

labor curve.

A second test used to address adequate labor is the review of the

uterine contraction pattern by determining adequacy of contractions

with use of an intrauterine pressure catheter.

Most importantly, the fetal heart tracing must be reassuring

throughout the labor course.

Procedures

Clinical pelvimetry, at a minimum, must address the angles of the spinous

processes (convergent, divergent, straight), the bi-ischial diameter (>8 cm),

the distance to the sacral promontory from the symphysis pubis (>12 cm),

and the relation of the bony pelvis to the fetal head.

Clinical pelvimetry requires experience and deliberate attention to the

question of pelvic adequacy. It cannot account for fetal size or

strength/frequency of contractions, but, in experienced hands, it may reliably

identify a pelvis as adequate, borderline, or contracted.

Medical Care

A prolonged latent phase (see Table in Background) is not indicative of

dystocia in itself because this diagnosis cannot be made in the latent phase.

Gabbe and colleagues state the following:

For those in the latent phase, the treatment of choice is rest for severalhours. During this interval, uterine activity, fetal status, and cervical


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effacement must be evaluated to determine if progress to the active phase

has occurred. Approximately 85% of patients so treated progress to the

active phase. Approximately 10% will cease to have contractions, and thediagnosis of false labor may be made. For the approximately 5% of patients

in whom therapeutic rest fails and in patients for whom expeditious delivery

is indicated, oxytocin infusion may be used.

Use of oxytocin for active management of labor is described in the

Medication section.

Limited studies have shown improvement in dysfunctional labor with use of a

beta-blocker. In cases of dysfunctional labor resulting from functional

dystocia or an abnormal uterine contractility pattern and in which oxytocin

implementation has not improved the outcome, a beta-blocker may be

considered. Low-dose administration of intravenous propranolol in abnormal

labor augmented with oxytocin reduced the need for cesarean delivery,

particularly among patients with inadequate uterine contractility.

Anecdotal reports have stated that simply repositioning the patient

frequently relieves a seemingly obstructed labor. Although not studiedrigorously, there appears to be little harm in this maneuver. In theory, it may

unseat an asynclitic or malrotated presenting part and allow it to engage in

the pelvis more effectively.

Surgical Care

Amniotomy is often used and has become an accepted practice once the

patient has reached the active phase of labor, although it has not been

shown to result in shorter labor. This practice is not recommended in the

latent phase of labor because it may only serve to increase the risk of

intrauterine infection or cord prolapse.

If one of the arrest or protraction disorders is identified and fails to respond

to conservative measures, or if the fetal heart pattern is nonreassuring,

expedient delivery is justified; this includes operative vaginal delivery (if

appropriate) or cesarean delivery as indicated. Operative delivery with use

of forceps or vacuum must be performed by an experienced provider. One

should be aware of the increased associations for shoulder dystocia and


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neonatal injury with operative vaginal delivery in the setting of abnormal

labor.

Medication Summary

A protocol called active management of labor can be applied to nulliparous

women with singleton cephalic presentations at term. This method involves

the use of high-dose oxytocin, with a starting rate of 6 mU/min and

increasing by 6 mU/min every 15 min to a maximum of 40 mU/min. The goal

is no more than 7 uterine contractions per 15 min. Under this protocol,

cesarean delivery is performed if vaginal delivery has not occurred or is not

imminent 12 hours after admission or for fetal compromise. Initially,

cesarean delivery rates were quoted at 4.8%, but it has since doubled, which

is attributed to widespread use of epidural anesthesia. Other studies using

the active management protocol describe cesarean delivery rates similar to

that of the low-dose protocol. Randomized clinical trials have shown that the

high-dose oxytocin regimens result in shorter labors than low-dose regimens

without adverse effects for the fetus.

Dinoprostone and misoprostol are prostaglandin analogs used to stimulatecervical dilation and uterine contractions; they are pharmacologic

alternatives to using laminaria or placing a Foley bulb in the cervix. Using

prostaglandin analogs with a scarred uterus (eg, from prior cesarean or

myomectomy) for labor induction is absolutely contraindicated due to the

significant risk for uterine rupture.

A randomized clinical trial testing the safety and efficacy of prostaglandin E2

(PgE2) as a treatment for dystocia in spontaneous labor revealed that asingle 1-mg dose of PgE2 vaginal gel is more effective than placebo in

resolving dystocia without increasing uterine hyperstimulation, but it may be

associated with an increase in the incidence of second stage cesarean

delivery.

Oxytocics

Oxytocin is the only US Food and Drug Administration (FDA)approved

medication recommended for labor augmentation. Other options include


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dinoprostone and misoprostol.

Produces rhythmic uterine contractions and can stimulate the gravid uterus.Has vasopressive and antidiuretic effects. Can also control postpartum

bleeding or hemorrhage. Has a half-life of 3-5 min, and reaches steady state

in approximately 40 min.

Beta-adrenergic blocking agents

Another option for abnormal labor secondary to inadequate uterine

contractility is a beta-blocker.

Complications

Maternal infection is a risk, especially when rupture of membranes

occurs for more than 18 hours. Administer antibiotics for signs and

symptoms of chorioamnionitis.

Fetal compromise can occur from the inability to tolerate labor (eg,

uterine hyperstimulation) or infection, and it must be closely

evaluated. Fetal heart monitoring often reveals signs of compromisewith decelerations, and fetal scalp pH is an option when indicated.

Probably the most common complication of the medical induction of

labor is hyperstimulation of the uterus. If unrecognized and

untreated, excessive stimulation of the uterus can result in fetal

compromise, cord compression, and uteroplacental insufficiency.

Uterine rupture, postpartum uterine atony, and postpartum

hemorrhage may occur and can be life-threatening complications

requiring emergent action.

Allen et al found that increased duration of the second stage of

laborin particular, duration longer than 3 hours in nulliparous

women and longer than 2 hours in multiparous womenincreases

the risk of both maternal and perinatal adverse outcomes. In their

population-based cohort study in 121,517 women (52% nulliparous),

women with a prolonged second stage were at increased risk for

obstetric trauma, postpartum hemorrhage, puerperal febrile

morbidity, and composite maternal morbidity, while their infants were

at increased risk for low 5-minute Apgar score, birth depression,

admission to the neonatal intensive care unit, and composite


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perinatal morbidity. Method of delivery modified the effect of duration

of second stage among nulliparous women only.

Prognosis

The prognosis of subsequent pregnancies depends on the cause for

abnormal labor. For example, if abnormal labor occurs from

macrosomia, the next infant may not be macrosomic. However, if the

abnormal labor was secondary to a contracted pelvis with a

normal-sized or small infant, then the likelihood for a recurrence of

abnormal labor is high.

In an attempt to determine whether increasing maternal age is more

commonly associated with dystocia, a study by Treacy et al

demonstrated that the incidences of oxytocin augmentation,

prolonged labor, instrument delivery, and intrapartum cesarean

delivery (including cesarean for dystocia) all increased significantly

and progressively with increasing maternal age. This study used an

established active management protocol, and oxytocin

augmentation proved a generally effective intervention in all age

categories. These findings have implications for the analysis of

intervention rates by health care providers, particularly in developed

countries where the proportion of older nulliparas is increasing.

A study by Zhu et al revealed that, with increasing interpregnancy

intervals, the risk for labor dystocia increases. Both functional and

mechanical dystocia were more prevalent in first births than in

subsequent births. In singleton births to multiparous mothers, labor

dystocia was associated with the interpregnancy interval in a

dose-response fashion. Compared with an interpregnancy interval ofless than 2 years, the adjusted odds ratios that was associated with

interpregnancy intervals of 2-3, 4-5, 6-7, 8-9, and 10+ years were

1.06, 1.15, 1.25, 1.31, and 1.50, respectively, when controlled for

other reproductive risk factors. Functional dystocia was associated

more strongly with interpregnancy interval than mechanical dystocia.

Patient Education

The patient must be aware of all risks involved with labor, including

the potential for emergent cesarean delivery if the fetus appears


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compromised. Furthermore, she should be kept informed of her

status throughout the labor course, especially if a change in

management is anticipated. Counsel patients early in pregnancy thatmaternal weight gain correlates with fetal weight gain, and excessive

gain and prepregnancy obesity are risk factors for abnormal labor.

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8.Dystocia