1. CHPTER 18 DYSTOCIA
부산백병원 산부인과
R1 이은숙

2. ABNORMAL LABOR AND FETOPELVIC DISPROPORTION

3. Etiological classification of 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

4. Dystocia 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

5. Dystocia 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

6. 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

7. 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

8. 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 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

9. 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

10. 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

11. 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)

12. Abnormal labor pattern
Diagnostic criteria
Nulliparas
Multiparas
Prolongation disorder
(Prolonged latent phase)
> 20 hr
>14hr
Protraction disorders
1. Protracted active phase dilatation
2. Protracted descent
< 1.2 cm/hr
< 1.0 cm/hr
< 1.5 cm/hr
< 2 cm/hr
Arrest disorders
1.Prolonged deceleration phase
2. Secondary arrest of dilatation
3. Arrest of descent
4. Failure of descent
> 3 hr
> 2 hr
> 1 hr
No descent in deceleration phase
or second stage

13. 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
increased

14. 1st & 2nd stage of normal labor

15. Inadequate labor Uterine dysfunction Fetopelvic disproportion
Ruptured membranes without labor

16. 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

17. 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

18. 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

19. 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)

20. 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)

21. 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.

22. 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)

23. Three anteroposterior diameters of the pelvic inlet

24. 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

25. Transverse diameter of the midpelvis

26. 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

27. Fetopelvic disproportion

28. 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

29. 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

30. Estimation of pelvic capacity
Computed tomographic scanning
Advantages
Reduction in radiation exposure
Greater accuracy
Easier to perform
Comparable cost
Magnetic resonance imaging
Lack of ionizing radiation
Accurate pelvic measurements
Complete fetal imaging
Providing the potential for evaluating reasons for soft tissue dystocia

31. 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.

32. 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

33. 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)

34. 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)

35. 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.

36. 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 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

37. 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)

38. 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

39. Maternal-fetal effects of dystocia
Maternal effects
Intrapartum infection
Uterine rupture
Pathological retraction ring
Fistula formation due to pressure necrosis
Pelvic floor injury

40. 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

41. Pathological retraction ring

42. Maternal-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

43. 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
->amniotomy
Progress is again assessed at 2 hours,
If not significant progress (i.e., 1 cm/hr)
-> high-dose oxytocin infusion

44. 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

45. Labor management protocols at Parkland Hospital

46. 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

47. 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

48. 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.

49. 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.