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CHPTER 18 DYSTOCIA. 부산백병원 산부인과 R1 이은숙. ABNORMAL LABOR AND FETOPELVIC DISPROPORTION. Etiological classification of dystocia. Dystocia literally, difficult labor abnormally slow progress of labor m/c contemporary indication of primary c/sec Abnormalities of the expulsive forces

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chpter 18 dystocia


부산백병원 산부인과

R1 이은숙

etiological classification of dystocia
Etiological classification of dystocia
  • Dystocia
    • literally, difficult labor
    • abnormally slow progress of labor
    • m/c contemporary indication of primary c/sec
  • Abnormalities of the expulsive forces
    • Uterine forces insufficiently strong or inappropriately coordinated to efface & dilate the cervix (uterine dysfunction)
    • Inadequate voluntary muscle effort during the second stage of labor
  • Abnormalities of presentation, position, or development of the fetus
  • Abnormalities of the maternal bony pelvis
  • Abnormalities of the reproductive tract that form an obstacle to fetal descent
  • Today, expression such as cephalopelvic disproportion

and failure to progress are often used to describe these dysfunctional labor when cesarean delivery is necessary

  • Cephalopelvic disproportion (CPD)
    • Disparity between the dimensions of the fetal head and maternal pelvis to preclude vaginal delivery
      • True CPD is rare and most CPD are due to malposition of the fetal head : asynclitism or extension of the bony diameters of the fetal head
      • Inability to achieve vaginal delivery after reaching complete dilatation is a significant marker of true dystocia because it is likely to recur
  • Failure to progress
    • This term include lack of progressive cervical dilatation or lack

of descent

    • The CPD and failure to progress are not precise terms and we should use more
    • Practical terms, such as protraction or arrest
    • The woman must be in the active phase of labor to diagnose either of these disorders
    • Active phase arrest in 5 % of term nulliparas, this incidence has not changed since the 1950s

( Freidman 1978, Handa and Laros 1993)

    • Inadequate uterine contractions ( < 180 Montevideo units )

were diagnosed in 80 % of women with active-phase arrest

overdiagnosis of dystocia
Overdiagnosis of dystocia
  • CPD (cephalopelvic disproportion)
    • Most disproportions are due to malposition of fetal head,

or to ineffective uterine contracture

  • Factors leading to increased use of c/sec for dystocia
    • Incorrect diagnosis of dystocia
    • Epidural analgesia
    • Fear of litigation
    • Obstetrician convenience
    • Variability in the criteria for diagnosis – major determinant
      • Almost 25% of the c/sec performed annually in the USA for the lack of progress were in women with cervical dilatation

of only 0 to 3 cm

labor diagnosis
Labor Diagnosis
  • The strict definition of labor - uterine contractions that bring about demonstrable effacement and dilatation of the cervix
  • Recognizing its start
    • to instruct the woman to quantify contractions for

some specified period

      • define labor onset as the clock time when painful contractions become regular : very subjective
    • to define the onset of labor to begin at the time of admission to the labor unit
      • Admission criteria ( by National Maternity Hospital in Dublin )
        • painful uterine contractions accompanied by any one of the following ;
        • ruptured membranes
        • bloody show
        • complete cervical effacement : in US, 3-4 cm or greater
normal labor
Normal labor
  • Criteria of Normal Labor

Concept of 3 functional divisions of labor by Friedman

  • Preparatory division
    • latent & acceleration phases
    • sensitive to sedation & conduction analgesia
    • little cervical dilatation occurs, but considerable changes take place in theground substance of cervix

(collagen & other connective tissue component)

  • Dilatational division
    • phase of maximum slope of cervical dilatation
    • most rapid rate of dilatation occur
    • unaffected by sedation or conduction analgesia
  • Pelvic division
    • deceleration phase & second stage
    • cardinal fetal movements in the cephalic presentation take place principally during this phase
normal labor1
Normal labor
  • Pattern of Cervical Dilatation ; 2 phases of cervical dilatation
  • Latent phase

subject to sensitive changes by extraneous factors

(sedation → prolongation, myometrial stimulation → shortening)

  • Active phase

① Acceleration phase

usually predictive of the outcome of a particular labor

② Phase of maximum slope

good measure of the overall efficiency of the machine

③ Deceleration phase

more reflective fetopelvic relationship

2nd stage of labor commences after complete cervical dilatation

→ only progressive descent of fetal presenting part is available

to assess the progress of labor

latent phase
Latent Phase
  • commences with maternal perception of regular contractions
  • accompanied by progressive & slow cervical dilatation and ends

at between 3 and 5 cm of dilatation

  • Prolonged latent phase
    • > 20 hr in the nullipara and > 14 hr in the parous woman
    • Factors that affect duration of the latent phase
      • excessive sedation or conduction analgesia
      • poor cervical condition
      • false labor
    • Management : rest and strong sedatives

-> 85 % begin active labor

-> 10 % cease contractions

-> 5 % recur an abnormal latent phase -> oxytocin stimulation

    • Amniotomy was discouraged during this phase
    • Fetal and Maternal Effect of prolongation : not influence morbidity and mortality
active labor
Active Labor
  • A rapid change in the slope of cervical dilatation between 3 & 4 cm

the mean duration of active phase labor in nulliparas was 4.9 hours

    • the rate of dilatation
      • 1.2 cm/hr is the minimum normal rate in the nullipara
      • 1.5 cm/hr is the minimum normal rate in the multipara
    • active labor phase abnormalities – m/c abnormalities of labor
      • incidence : in nullipara, 25% vs in multipara, 15%
      • classification : protraction, arrest (Friedman 1972)
      • associated factors of active labor phase abnormalities

. excessive sedation or conduction analgesia

. fetal malposition (e.g., persistent occiput posterior)

  • The majority of active phase disorders did not result in cesarean delivery -only about 2 % of the 500 women studies (Friedman 1955)
second stage of labor
Second Stage of Labor
  • begin when cervical dilatation is complete and ends with fetal expulsion
  • median duration : in nulliparas - 50 min, in multiparas - 20 min
  • average second stage labor was lengthened about 25 minutes

by regional analgesia

  • limit of the length of the second stage
    • in nulliparas : 2 hrs & extended to 3 hrs when regional analgesia
    • in multiparas : 1 hr & extended to 2 hrs with regional analgesia
  • The relationship between the duration of second stage labor and pregnancy outcome
    • maternal effects : postpartum hemorrhage & infection increased but incidence is quite small
    • infant effects
  • They concluded that there is no compelling reason to intervene with

a possibly difficult forceps or vacuum extraction but after 3 hours in

the second stage, delivery by cesarean or other operative method


inadequate labor
Inadequate labor
  • Uterine dysfunction
  • Fetopelvic disproportion
  • Ruptured membranes without labor
uterine dysfunction
Uterine Dysfunction
  • Characterized by lack of progress
  • In the latent phase, the diagnosis is difficult
  • One of the most common errors is to treat women for uterine dysfunction who are not yet in active labor
  • There have been three significant advances in the treatment of uterine dysfunction:
    • improvement of perinatal morbidity and mortality
    • dilute intravenous infusion of oxytocin
    • more frequent use of cesarean delivery rather than difficult midforceps delivery
uterine dysfunction1
Uterine Dysfunction
  • The lower limit of contraction pressure required to dilate

the cervix is 15 mmHg (Caldeyro-Barcia, 1950)

  • Normal spontaneous contractions often exert pressures of about 60 mmHg (Hendricks,1959)
  • Two types of uterine dysfunctions
    • hypotonic uterine dysfunction
    • hypertonic uterine dysfunction or incoordinate uterine dysfunction
types of uterine dysfunction
Types of uterine dysfunction
  • Hypotonic uterine dysfunction
    • There is no basal hypertonus
    • Uterine contractions have a normal gradient pattern (synchronous)
    • The slight rise in pressure during a contraction is insufficient

to dilate the cervix.

  • Hypertonic uterine dysfunction
    • Basal tone is elevated appreciably
    • the pressure gradient is distorted
    • perhaps by contraction of the midsegment of the uterus with more force than the fundus
    • by complete asynchronism of the impulses originating

in each cornu

    • a combination of these two
reported causes of uterine dysfunction
Reported causes of uterine dysfunction
  • Epidural analgesia
    • Lengthening of both first- and second-stage labor as well as slowing of the rate of fetal descent
  • Chorioamnionitis
    • Maternal intrapartum infection plays a role in the development of abnormal uterine activity
  • Maternal position during labor
    • Walking during labor have been reported to shorten labors, decrease the need for augmentation with oxytocin, decrease

the need for analgesia, and lower the frequency of instrumental vaginal delivery

    • Contraction frequency & intensity have been reported to increase with sitting or standing (Miller 1983)
    • Uterine contractions occur more frequently but with less intensity in the supine position compared with lying on her side.
    • There is no conclusive evidence that upright maternal posture or ambulation improves labor (Lupe and Gross 1986)
reported causes of uterine dysfunction1
Reported causes of uterine dysfunction
  • Birthing position in second-stage labor
    • Russell(1969) described a 20 to 30 percent increase in the

area of the pelvic outlet with squatting compared with the

supine position

    • Crowley (1991) compared to deliver in an obstetrical birth chair with to deliver in bed : there were no advantages with use of the birthing chair, but hemorrhage was increased in the group.
    • De jong(1997) found no increase in hemorrhage with the sitting position
    • The benefits of the upright position : less maternal pain and enhanced maternal satisfaction with the birthing experience
  • Immersion in water
    • Advocated as a means of relaxation (Odent, 1983)
    • Not alter the rate the rate of cervical dilatation, length of labor, route of delivery, or analgesia use (Schorn, 1993)
fetopelvic disproportion
Fetopelvic disproportion
  • This arises from either diminished pelvic size, excessive

fetal size, or more usually, a combination of both.

  • Pelvic capacity
    • Any contraction of the pelvic diameters that diminishes
    • the capacity of the pelvis can create dystocia
    • Contractions of the pelvic inlet, the midpelvis, the pelvic outlet and combinations of these.
fetopelvic disproportion1
Fetopelvic disproportion
  • Contracted Pelvic Inlet
    • Definition
      • AP diameter < 10 cm

or transverse diameter < 12 cm

      • Diagonal conjugate < 11.5 cm
    • Both AP diameter(< 10cm) and transverse diameter (< 12cm)

are contracted -> dystocia is much greater

    • Cervical dilatation is facilitated by hydrostatic action of the unruptured membranes or, after their rupture, by direct application of the presenting part against the cervix.
    • In contracted pelvis, however, when the head is arrested in the pelvic inlet, the entire force exerted by the uterus acts directly upon the portion of membranes that overlie the dilating cervix.
    • Consequently, early spontaneous rupture of the membranes is more likely to result.
    • Fetal presentation and position
      • face and shoulder presentation ( x3) & cord prolapse ( x4-6)
fetopelvic disproportion2
Fetopelvic disproportion
  • Average midpelvis measurements
    • Transverse (interspinous) 10.5cm
    • Anteroposterior (from the lower border of the symphysis pubis to the junction of the fourth and fifth sacral vertebrae) 11.5cm
    • Posterior sagittal (from the midpoint of the interspinous line to the same point on the sacrum) 5cm
  • Contracted Midpelvis
    • Definition
      • The interischial spinous diameter

+ posterior sagittal diameter < 13.5 cm

      • The interischial spinous diameter < 8 cm
    • Suggestive findings
      • The ischial spines are prominent
      • The pelvic side walls converge
      • The sacrosciatic notch is narrow
fetopelvic disproportion3
Fetopelvic disproportion
  • Contracted Pelvic Outlet
  • Definition
    • The interischial tuberous diameter < 8 cm
    • Outlet contraction without concomitant midplane contraction

is rare.

  • Prognosis
    • Diminution in the intertuberous diameter with consequent narrowing of the anterior triangle must inevitably force the fetal head posteriorly.
    • Depend on the size of the posterior triangle

on the interischial tuberous diameter& posterior sagittal diameter of outlet

    • Production of perineal tears
pelvic fractures and rare pelvic contraction
Pelvic fractures and rare pelvic contraction
  • Trauma from automobile collisions: most common cause of pelvic fractures
  • Bilateral fractures of the pubic rami :compromise of birth canal capacity by callus formation or malunion
  • Careful review of previous of previous x-ray and possibly computed tomographic pelvimetry later in pregnancy, unless c/sec is performed for another reason.
  • Rare pelvic contraction : dwarfs, poliomyelitis, kyphoscoliosis
estimation of pelvic capacity
Estimation of pelvic capacity
  • Clinical estimation
    • Narrow pelvic arch (<90 degrees) : narrow pelvis
    • Unengaged fetal head -> excessive fetal head size or reduced pelvic inlet capacity
  • X-ray pelvimetry
    • 5 factors that determines successful vaginal deliveries.
      • size and shape of the bony pelvis
      • size of fetal head
      • force of uterine contractions
      • moldability of the fetal head
      • presentation and position of the fetus
    • Indications for X-ray pelvimetry
      • for trial of vaginal delivery in case of breech presentation and previous injury or disease likely to affect bony pelvis
estimation of pelvic capacity1
Estimation of pelvic capacity
  • Computed tomographic scanning
    • Advantages
      • Reduction in radiation exposure
      • Greater accuracy
      • Easier to perform
      • Comparable cost
  • Magnetic resonance imaging
    • Advantages
      • Lack of ionizing radiation
      • Accurate pelvic measurements
      • Complete fetal imaging
      • Providing the potential for evaluating reasons for soft tissue dystocia
excessive fetal size
Excessive fetal size
  • Although the fetal weight threshold decreased from 5000g to 4500g, has been that fetal size seldom is a suitable explanation for failed labor.
  • The greatest obstetrical concern was not that the fetal head might fail to traverse the pelvic passage, but, rather that the shoulders might not fit through the pelvic inlet or outlet.
  • Selection of a fetal size threshold to predict fetopelvic disproportion and prevent obstructed labor, is not possible because most cases of disproportion occur in fetuses whose weight is well within the range of the general obstetric population.
  • Two thirds of infants requiring c/sec at Parkland Hospital after an attempt at forceps delivery failed, weighed less than 3700g
    • Thus, fetopelvic disproportion usually is not associated with excessive fetal size.
estimation of fetal head size
Estimation of fetal head size
  • Clinical estimation - Muller method
    • In an occiput presentation, the brow and the suboccipital region are grasped through the abdominal wall with the fingers and firm pressure is directed downward in the axis

of the inlet.

    • Fundal pressure by an assistant usually is helpful.
    • The effect of the forces on the descent of the head can be evaluated by concomitant vaginal examination.
  • No disproportion -> the head readily enters the pelvis, and vaginal delivery can be predicted.
  • Inability to push the head into the pelvis does net necessarily indicate that vaginal delivery is impossible.
  • Flexed fetal head that overrides the symphysis pubis -> presumptive evidence of disproportion
  • No relation between dystocia and failure of descent of the head
ruptured membranes without labor
Ruptured membranes without labor
  • Membrane rupture without spontaneous uterine contractions occurs in about 8 % of terms
  • Management
    • stimulation of contractions when labor did not begin after 6 to

12 hours because of amnionitis

    • Almost 75 % of those observed entered labor spontaneously within 24 hours
  • The cesarean delivery rate was almost tripled in women undergoing labor induction ( Duff 1984 )
  • In contrast, there was no advantage to delaying intervention because of neonatal infections ( Wagner 1989 )
  • Prostaglandin E2 to reduce the admission-to-delivery interval in non-laboring women after membrane rupture at term

(Chua 1995, Mahood and Dick 1995)

  • Labor induction with intravenous oxytocin was the preferred management (Hannah 1996)
diagnosis of inadequate labor
Diagnosis of inadequate labor
  • Active-phase disorders : neither failure to progress nor cephalopelvic disproportion are precise terms (ACOG, 1995)
  • A more practical classification is to divide labor abnormal into either slower-than-normal (protraction disorder) or complete cessation of progress (arrest disorder).
  • The woman must be the active phase of labor (cervix dilated 3 to 4 cm or more) to diagnose either these.
  • Active-phase arrest( no dilatation for 2 hours or more) in 5 percent of term nulliparas.
  • Inadequate uterine contractions, defined as less than 180 Montevideo units were diagnosed in 80 percent of women with active-phase arrest.
  • A labor management in which protraction is defined as less than 1cm/hr cervical dilatation for a minimum of 4 hours. (WHO,1994)
diagnosis of active phase labor disorders
Diagnosis of Active Phase Labor Disorders
  • To effectively induce or augment labor with oxytocin, 90 percent

of women achieve 200 to 225 Montevideo units, and 40 percent

achieve at least 300 Montevideo units.

  • Before the diagnosis of arrest during first stage labor is made,

both of these criteria should be met :

    • The latent phase has been completed, with the cervix dilated 4cm or more.
    • A uterine contraction pattern of 200 Montevideo units or

more in a 10-minute period has been present for 2 hours without cervical change

      • 2-hour rule on the grounds that a longer time, i.e.,

at least 4 hours, is necessary before concluding that the

active phase of laber has failed.

fetal station at onset of active labor
Fetal station at onset of activelabor
  • Both protraction and arrest labor disorders in women with fetal head stations above +1cm & that the higher the station at the onset of labor in nulliparas, the more prolonged the labor. (Friedman and Sachtleben , 1965)
  • The fetal station at the time of arrested labor was also a risk factor for dystocia.
  • The prognosis for dystocia ,however, was not related to incremen- tally higher fetal head stations above the pelvic midplane (0 station)
  • 86 percent of nulliparous women without fetal head engagement at diagnosis of active labor delivered vaginally.
  • Thus, lack of engagement at the onset of labor, although a statistical risk factor for dystocia, should not be assumed to necessarily predict fetopelvic disproportion
second stage disorder
Second-stage disorder
  • With achievement of full cervical dilatation, the great majority of women cannot resist the urge to “ bear down” or “push” each time the uterus contract
  • Coaching women to push forcefully, compared with letting them follow their own urge to bear down, has been reported to offer no advantage (Parnell , 1993)
cause of inadequate expulsive forces
Cause of inadequate expulsive forces
  • Heavy sedation or conduction analgesia-lumbar epidural, caudal,

or intrathecal-are likely to reduce the reflex urge to push, and at the same time may impair ability to contract the abdominal muscles sufficiently.

  • Careful selection of the kind analgesia & timing of its administration

are important to avoid comprise of voluntary expulsive efforts.

  • Continuous epidural analgesia -> the paralytic efforts to wear off

so that the woman can generate intra-abdominal pressure sufficient

to move the fetal head into position appropriate for outlet forceps


  • For the woman who cannot bear down appropriately with each contraction because of great discomfort, analgesia is likely to be

of considerable benefit

maternal fetal effects of dystocia
Maternal-fetal effects of dystocia
  • Maternal effects
    • Intrapartum infection
    • Uterine rupture
    • Pathological retraction ring
    • Fistula formation due to pressure necrosis
    • Pelvic floor injury
differentiation of uterine activity
Differentiation of Uterine Activity
  • During active labor, uterus differentiates into 2 distinct parts
  • Upper segment
    • actively contracting , becomes thicker as labor advances
    • quite firm or hard on abdominal palpation1
  • Lower segment
    • relatively passive
    • develops into a much thinly walled passage for the fetus
    • much less firm on abdominal palpation
  • Physiologic retraction ring :
    • As labor progresses -> thinning of the lower uterine seg-

ment and the concomitant thickening of upper segment ->

the boundary between the two is marked by a ridge on inner

uterine surface

  • Pathologic retraction ring (the ring of Bandle)
    • In obstructed labor -> lower uterine segment’s extreme thinning

-> the ring is very prominent

maternal fetal effects of dystocia1
Maternal-fetal effects of dystocia
  • Fetal effects of dystocia
    • Prolonged membrane rupture & intrauterine infection
    • Caput succedaneum
      • The caput may reach almost to the pelvic floor while the

head is not engaged.

    • Fetal head molding
      • Tentorial tears, laceration of fetal blood vessels and

fetal intracranial hemorrhage

labor management protocols
Labor Management Protocols
  • Active management of labor (O'Driscoll 1984)

: amniotomy and oxytocin

    • Labor is diagnosed : painful uterine contractions + complete cervical dilatation, bloody show, or ruptured membranes
    • Pelvic examination :
      • Performed each hour for the next 3 hours

-> at 2 hour intervals

      • When dilatation has not increased by at least 1 cm


      • Progress is again assessed at 2 hours,
      • If not significant progress (i.e., 1 cm/hr)

-> high-dose oxytocin infusion

parkland hospital labor management protocol
Parkland Hospital Labor Management Protocol
  • Pelvic examinations be performed approximately every 2 hours
  • When the cervix does not dilate within about 2 hours of admission

-> amniotomy

  • In women whose labors do not progress

-> an intrauterine pressure catherter

  • Hypotonic contractions and no cervical progress

-> high-dose oxytocin regimen

    • Cesarean rates in nulliparous and parous women were 8.7 and 1.5 %, respectively
    • These labor interventions and the relatively infrequent use of cesarean delivery did not jeopardize the fetus-newborn infant
precipitate labor and delivery
Precipitate labor and delivery
  • Definition
    • Expulsion of the fetus in less than 3 hours
  • Causes
    • An abnormally low resistance of the soft parts

of the birth canal

    • Abnormally strong uterine and abdominal contractions
    • The absence of painful sensations
precipitate labor and delivery1
Precipitate labor and delivery
  • Maternal effects
    • Uterine rupture
    • Extensive lacerations of the cervix, vagina, vulva, or perineum
    • Amnionic fluid embolism
    • Postpartum hemorrhage from uterine atony
precipitate labor and delivery2
Precipitate labor and delivery
  • Effects on fetus and neonate
    • Increased perinatal mortality and morbidity
    • Intracranial trauma
    • Erb-Duchenne palsy
    • The infant may fall to the floor and be injured.
    • Resuscitation is not immediately available.
precipitate labor and delivery3
Precipitate labor and delivery
  • Treatment
    • The use of tocolytic agents such as magnesium sulfate is unproven in these circumstances.
    • Use of general anesthesia with agents that impair uterine contractibility is often excessively heroic.
    • Certainly, any oxytocin agents being administered should be stopped immediately.