CHPTER 18 DYSTOCIA
부산백병원 산부인과
R1 이은숙
ABNORMAL LABOR
AND
FETOPELVIC DISPROPORTION
Etiological classification of dystocia
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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
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Dystocia
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Today, expression such as cephalopelvic disproportion
and failure to progress are often used to describe these
dysfunctional labor when cesarean delivery is necessary
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Cephalopelvic disproportion (CPD)
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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
Dystocia
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Failure to progress
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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
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CPD (cephalopelvic disproportion)
 Most disproportions are due to malposition of fetal head,
or to ineffective uterine contracture
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Factors leading to increased use of c/sec for dystocia
 Incorrect diagnosis of dystocia
 Epidural analgesia
 Fear of litigation
 Obstetrician convenience
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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
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The strict definition of labor - uterine contractions that bring about
demonstrable effacement and dilatation of the cervix
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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
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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 the ground 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
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Normal labor
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Pattern of Cervical Dilatation ; 2 phases of cervical dilatation
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Latent phase
subject to sensitive changes by extraneous factors
(sedation → prolongation, myometrial stimulation → shortening)
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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
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
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Active Labor
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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)
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The majority of active phase disorders did not result in cesarean
delivery -only about 2 % of the 500 women studies (Friedman 1955)
Abnormal labor pattern
Labor pattern
Diagnostic criteria
Nulliparas
Multiparas
> 20 hr
>14hr
1. Protracted active phase dilatation
< 1.2 cm/hr
< 1.5 cm/hr
2. Protracted descent
< 1.0 cm/hr
< 2 cm/hr
> 3 hr
> 2 hr
> 1 hr
No descent in deceleration phase
or second stage
> 1 hr
> 2 hr
> 1 hr
Prolongation disorder
(Prolonged latent phase)
Protraction disorders
Arrest disorders
1.Prolonged deceleration phase
2. Secondary arrest of dilatation
3. Arrest of descent
4. Failure of descent
Second Stage of Labor
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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
increased
1st & 2nd stage of normal labor
Inadequate labor
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Uterine dysfunction
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Fetopelvic disproportion
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Ruptured membranes without labor
Uterine Dysfunction
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Characterized by lack of progress
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In the latent phase, the diagnosis is difficult
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One of the most common errors is to treat women for uterine
dysfunction who are not yet in active labor
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There have been three significant advances in the treatment
of uterine dysfunction:
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improvement of perinatal morbidity and mortality
dilute intravenous infusion of oxytocin
more frequent use of cesarean delivery rather than difficult
midforceps delivery
Uterine Dysfunction
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The lower limit of contraction pressure required to dilate
the cervix is 15 mmHg (Caldeyro-Barcia, 1950)
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Normal spontaneous contractions often exert pressures of
about 60 mmHg (Hendricks,1959)
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Two types of uterine dysfunctions
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hypotonic uterine dysfunction
hypertonic uterine dysfunction or incoordinate uterine
dysfunction
Types of uterine dysfunction
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Hypotonic uterine dysfunction
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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
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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
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)
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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)
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Fetopelvic disproportion
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This arises from either diminished pelvic size, excessive
fetal size, or more usually, a combination of both.
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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 disproportion
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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)
Three anteroposterior diameters of
the pelvic inlet
Fetopelvic disproportion
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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
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Contracted Midpelvis
 Definition
 The interischial spinous diameter
+ posterior sagittal diameter < 13.5 cm
 The interischial spinous diameter < 8 cm
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Suggestive findings
 The ischial spines are prominent
 The pelvic side walls converge
 The sacrosciatic notch is narrow
Transverse diameter of the midpelvis
Fetopelvic disproportion
Contracted Pelvic Outlet
 Definition
 The interischial tuberous diameter < 8 cm
 Outlet contraction without concomitant midplane contraction
is rare.
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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
Fetopelvic disproportion
Pelvic fractures and rare pelvic contraction
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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
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Clinical estimation
 Narrow pelvic arch (<90 degrees) : narrow pelvis
 Unengaged fetal head -> excessive fetal head size or reduced
pelvic inlet capacity
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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 capacity
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Computed tomographic scanning
 Advantages
 Reduction in radiation exposure
 Greater accuracy
 Easier to perform
 Comparable cost
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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
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
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Thus, fetopelvic disproportion usually is not associated with
excessive fetal size.
Estimation of fetal head size
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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
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
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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)
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Diagnosis of inadequate labor
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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
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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.
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Before the diagnosis of arrest during first stage labor is made,
both of these criteria should be met :
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The latent phase has been completed, with the cervix dilated 4cm
or more.
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A uterine contraction pattern of 200 Montevideo units or
more in a 10-minute period has been present for 2 hours without
cervical change
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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
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 incrementally 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.
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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
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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
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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
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
delivery.
 For the woman who cannot bear down appropriately with each
contraction because of great discomfort, analgesia is likely to be
of considerable benefit
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Maternal-fetal effects of dystocia
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Maternal effects
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Intrapartum infection
Uterine rupture
Pathological retraction ring
Fistula formation due to pressure necrosis
Pelvic floor injury
Differentiation of Uterine Activity
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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 segment 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
Pathological retraction ring
Maternal-fetal effects of dystocia
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Fetal effects of dystocia
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Prolonged membrane rupture & intrauterine infection
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Caput succedaneum
 The caput may reach almost to the pelvic floor while the
head is not engaged.
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Fetal head molding
 Tentorial tears, laceration of fetal blood vessels and
fetal intracranial hemorrhage
Labor Management Protocols
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Active management of labor (O'Driscoll 1984)
: amniotomy and oxytocin
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Labor is diagnosed : painful uterine contractions + complete
cervical dilatation, bloody show, or ruptured membranes
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Pelvic examination :
 Performed each hour for the next 3 hours
-> at 2 hour intervals
 When dilatation has not increased by at least 1 cm
->amniotomy
 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
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
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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
Labor management protocols
at Parkland Hospital
Admission
Cervix 4cm
2 to 3 hours depending on parity
Amniotomy
2 hours
Internal contraction monitor
3 hours
Oxytocin
2 to 4 hours depending on parity
Delivery
Precipitate labor and delivery
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Definition
 Expulsion of the fetus in less than 3 hours
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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 delivery
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Maternal effects
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Uterine rupture
Extensive lacerations of the cervix, vagina, vulva, or
perineum
Amnionic fluid embolism
Postpartum hemorrhage from uterine atony
Precipitate labor and delivery
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Effects on fetus and neonate
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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 delivery
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Treatment
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The use of tocolytic agents such as magnesium sulfate
is unproven in these circumstances.
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Use of general anesthesia with agents that impair uterine
contractibility is often excessively heroic.
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Certainly, any oxytocin agents being administered should
be stopped immediately.