Dystocia due to Abnormalities of the Expulsive Forces

Chapter 17. Dystocia due to Abnormalities of the Expulsive Forces

1ST year resident J.W. Lee. M.D.

I. Introduction

  • Dystocia ; difficult labor → Abnormal progress in labor.

  • 4 Distinct abnormality (in singly or combination)

    1. Abnormality of the Expulsive force.
    2. Abnormality of the presentation, position, development of fetus.
    3. Abnormality of the maternal bony pelvis.→ pelvic contraction.
    4. Abnormality of the birth canal. → obstacle to fetal descent.

  • As a generalization, Uterine dysfunction → common whenever there is disproportion between the
    presenting part & birth canal.

  • Primary Cesarean delivery Ix.

    1st : Dystocia (43%)

    2nd : Fetal distress (14%)

II. Labor Diagnosis

  • Strict definition of Labor

    ; Uterine contraction (UC) + demonstrable efface & dilatation of Cervix.

  • Criteria for Adm. at term → Dublin ; not used

    1. ROM
    2. Bloody show + UC (painful)
    3. Complete Cervical effacement

  • in US. based on the extent of cervical dilatation accompanied by painful uterine contraction

    : painful UC, intact membrane, cervix 3∼4cm↑

    --> reasonably reliable threshold for the diagnosis of active Labor.

    cf. the woman's perceptions of what is or is not labor largely influence the diagnosis of the labor.

1. lst stage of labor

  • 1st stage : UC (active) --> Cervical full dilatation (Stage of cervical effacement & dilatation)
  • Labor : never let the sun set twice on a laboring woman.
  • Friedman - 3 functional division of labor

    Figure 17-2
    I. Preparatory division ← little cervical dilatation

    • change in the ground substance (collagen) & other cervical connective tissue component.
    • Sensitive to sedation & conduction analgesia.

    II. Dilatational division - most rapid rate.

    • Unaffected by sedation & conduction analgesia

    III. Pelvic division ;

    • deceleration phase of cervical dilatation, Cardinal movement.

      Figure 17-3

    (I) Latent phase

    • Onset : as the point at which the mother perceives regular contraction.
    • Cervical softening & efface.
    • Minimum criteria for subsequent entry into the active phase of labor.

      Cervical dilatation rate : Nulli - 1.2cm/hr

      Multi - 1.5cm/hr

    • latent phase commences with maternal perception of regular contraction, and the presence
      of progressive, albeit slow, cervical dilatation ends at between 3∼5cm, which is the threshold for
      active phase transition.

    • Prolonged latent phase

      : Nulli - 20hr ↑

      Multi - 14hr ↑

      cf) Statistical maximum

      1. Primi -- 20hr (mean duration : 8.6hr)

      2. Multi -- 14hr

        -- with the majority of woman exhibiting much shorter latent phase.

    • Factors that affect duration of latent phase.

      • Excessive sedation / conduction analgesia
      • Poor cervical condition. (eg. thick uneffaced, undilated)
      • False labor

        • Friedman ; either rest / oxytocin stimulation → equally efficacious & safe in correcting prolonged
          latent phases.

        • Rest was preferable to active intervention because of the frequency of unrecognized false labor.
          by strong sedatives : 85% -- commence active labor during or after awakening.

          10% -- cease contracting ( --> false labor )

          5% -- recurrence of abnormal latent phase (required oxytocin stimulation)

        • Prolongation of the latent phase did not adversely influence fetal or maternal morbidity
          or mortality and cautioned against C/sec as a primary therapy.

        • Friedman's latent phase took place over the approximately 3 wks antedating active labor requiring
          hospital admission.

      (II) Active labor

      • Rapid change in the slope of cervical dilatation between 3 - 4cm

        Figure 17-3

      • Active phase of labor.; most rapid rated of cervical dilatation consistently begins when the cervix is
        3∼4cm dilated.

      • In the presence of UC, cervical dilatation of 3∼4cm or more ; threshold for the active phase of labor.

      • Mean duration of active phase labor

      • Nulli : 4.9hr → 1.2cm/hr (minimal normal rate) cf) 11.7hr (statistical max.)
        Multi : 1.5cm/hr

      • Friedman : active phase ended at 8∼9cm where there was deceleration of cervical dilatation.

      • Primi : enter the active phase at 3∼4cm, expected to reach 8∼10cm. within 3∼4hr.

        ex) cervical dilatation : 4cm → complete dilatation (4hr)

      • Primi (25%), Multi (15%) -- complicated by active phase abnormality

        : active phase disorders are the most common abnormalities of labor.

        Table 17-1.

      • Descent ; begin in the later stage of active cervical dilatation and commences at about 7∼8cm in
        primi and become most rapid after 8cm.

      • Subdivision of active cervical dilatation

        1) Protraction: slow rate of cervical dilatation or descent

        2) Arrest: complete cessation of cervical dilatation or descent

        Factors contributing to both protraction and arrest is CPD, excessive sedation, conduction
        analgesia and fetal malposition (ex. POP).

        cf. Friedman's "latent phase" actually occurred over several weeks preceding active labor.
        Hendricks : at admission → 2∼4cm.

        to complete cervical dilatation : Multi - 3.2hr

        Nulli - 4.8hr

2. 2nd stage of Labor

  • Cervical full dilatation - expulsion of fetus (stage expulsion of fetus)

  • Median duration Nulli ; 50min.
    Multi ; 20min. but highly variable.

  • Higher parity with a previously dilated vagina and perineum, 2 or 3 expulsive efforts after full
    dilatation --> complete delivary.

  • 2nd stage rules that limit its duration.

    : Current recommendation for the length of 2nd stage

    in Nulli ; 2hr. / → 3hr when conduction analgesic (+)

    in Multi ; 1hr / → 2hr. when conduction analgesic (+)

  • At the Johns Hopkins Hospital

    (Relationship between the duration of second stage labor & pregnancy outcome)

    • Prophylactic forceps delivary was practiced.

    • A total of 8% women were deliveried after 2hr in second stage

    • Common cause : POP

    • Interresting feature of pregnancy with a prolonged second stage : excessive duration ( beyond
      20min ) of dilatational division of labor

    • 2nd stage prolongation (up to 2hr)

      : postpartum hemorrhage & infection↑→ but quite small, but not ↑ infant mortality.

      ∴ Epidural analgesia commonly used.

      ∴ American colleague of Ob & Gyn

      --> permitting and additional hour for the 2nd stage when conduction analgesia is used.

3. Spontaneous labor and delivery

  • How long is normal spotaneous labor & delivery 

    • Kilpatrick

      ⇒ labor onset defined (determined by Pt,s history)

      : time when regular, painful UC (every 3∼5') and leading to cervical change.

      Mean length of parturition

      → Primi : 9hr without conduction analgesia / 95tile upper limit - 18.5hr

      Multi : 6hr without conduction analgesia / 95tile upper limit - 13.5hr

    • At admission ; Parity & cervical dilatation
      → significant determinant of the length of
      spontaneous parturition.

      cf. at admission, 80% of women were admitted with cervical dilatation of 5cm or less
      mean time (Adm. - Delivery) → 3.5hr. (95% --> within 10.1hr)

      : suggest normal human parturition → relatively short in duration.

4. Summary

  • Active labor : reliably diagnosed when cervical dilatation is 3cm↑ in presence of UC
    Once this cervical dilatation threshold is reached, normal progress to delivery can be expected,
    depending in the ensuing 4 to 6 hr or so.

  • When time breaches in normal labor boundaries are the only pregnancy complication, interventions
    other than C/sec must be considered thoroughly before resorting to this method of delivery for failure
    to progress.

  • Insufficient UC is a common & correctable cause of abnormal labor progress.

III. Uterine Dysfunction

1. Introduction

  • Descent normally begins well before the cervical reaches full dilatation & proceeds until the P.P.
    reaches the perineum.→ highly variable.

  • 3 Significant advances in the treatment of uterine dysfunction

    1. Realization that undue prolongation of labor may contribute to perinatal morbidity & mortality.
    2. Use of very dilute IV oxytocin in the treatment of certain types of uterine dysfunction.
    3. More frequent use of C/sec rather than difficult midforceps delivery when oxytocin fails or its use is

2. Types of Dysfunction

  • UC of normal labor ; gradient of myometrial activity being greatest & lasting longest at the fundus
    (fundal dominance) & diminishing toward the cervix.

  • The Montevideo group study

    • Lower limit of contraction pre. required to dilate cervix ; 15mmHg.

      cf. Normal spontaneous contraction after exert pressure of about 60mmHg

  • 2 types of uterine dysfunction.

    I. Hypotonic uterine dysfunction.

    • no basal hypertonus / uterine contraction - normal gradient pattern (Synchronous).
    • occurs during the active phase. after cervix has dilates to more than 4cm.

    II. Hypertonic uterine dysfunction / Incoordinate uterine dysfunction.

    • basal tone↑/ pre. gredient - distorted.
    • perhaps by contraction of the midsegment of uterus with more force than the fundus or by complete
      asynchronism of the impulses originating in each cornu, or a combination of these two
    • in the latent phase.
    • favorably to treatment with oxytocin

  • "Adequate labor" ; wide range of Ut. activities

    • amplitude of each contraction ; 25∼75mmHg & contractions occur over a total of 2∼4.5min in
      every 10min. window, achieving 95 - 395 Montevideo unit.

      Figure 17-5

3. Etiology

  • Common cause ; pelvic contraction & fetal malposition.

    • moderate degrees of pelvic contraction & fetal malposition → cause hypotonic uterine dysfunction

      ; great clinical importance.

    • ex) Overdistention of the uterus. (twin, hydramnios)

      Elderly nullipara ; cervical fibrosis.

    • but, in many, perhaps 1/2 : unknown

4. Complication

    1) Fetal & neonatal death <-- intrauterine infection

    2) Maternal exhaustion

    3) Maternal psychological scar

    4) Definite deleterious effect upon future childbearing

IV. Dystocia

  • Broad category ; CPD & failure to progress.

    1) Absolute CPD

    : disparity between size of maternal pelvis & fetal head that precludes vag. delivery whether or not the
    fetal head presents optimal bony diameters.

    2) Relative CPD

    : asynclitism or extension of the fetal head presents bony diameter too great to allow passage through
    the maternal pelvis

    3) Failure to progress

    : lack of progressive cervical dilatation or lack of descent of the fetal head.

    → excessive fetal size, malpresentation, insufficient uterine expulsive forces.

1. Overdiagnosis

    d/t Obstetrician convenience, incorrect diagnosis, fear of litigation.

2. Diagnosis

  • ACOG suggested that, before the diagnosis of arrest in the lst stage of labor is made, both or these
    criteria should be met :

    • the latent phase of labor has been completed with cervix dilated 4cm or more.
    • UC pattern of 200 Montevideo unit or more in a 10-min period has been present for 2hr without
      cervical change.

  • Active Management of Labor.

    ; solutions for unnecessary C/S for dystocia.

    • Labor is diagnosed when painfu UC are companied by complete cervical effacement, bloody show, or
      ROM ; Women with such findings are committed to delivery within 8 hr

    • The onset of labor is considered to begin with admission.

      Pelvic exam is performed at regular intervals of 1hr for next 3hr. and thereafter at 2hr interval.

      Progress is assessed for the lst time 1hr after admission.

      When dilatation has not increased by at least 1cm. amniotomy is performed.

      Progress is assessed for the 2nd time at 2hrs after admission.

      An oxytoin infusion is started at this time unless significant progress (1cm/hr) has occured.

    • if ROM (+), Oxytocin is begun for no progress at the 1hr mark.

    • Labor is divided into a latent phase, should last no longer than 8hr, and active phase starting at 3cm
      cervical dilatation the rate of which should be no slow than 1cm/hr.

    • A 4hr wait (lag time) is recommended before intervention when the active phase of labor is slow.

3. Maternal Position during Parturition

  • UC occurs more frequently but with less intensity with the mother in the supine position compared
    with lying on her side.

    Conversely, sitting or standing --> UC frequency & intensity inc.

  • No conclusive evidence that upright maternal posture or ambulation during the 1st stage improves

V. Treatment of insufficient Uterine activity

  • 2 Questions must be answered before a treatment plan can be formulated 

    1. Has the woman actually been in active labor 
    2. Is there CPD 

  • Uterine dysfunction : protection against pelvic contraction , uterus does not typically persist in
    spontaneous activity that would lead to rupture.

    1. Diagnosis of active labor,
    2. Head is well fixed in the pelvis.
    3. if membrane is intact --> amniotomy, close observation for 30-60min d/t cord prolapse.
    4. Ideally intrauterine pressure catheter & fetal scalp electrode placed
    5. Decision must be made whether to stimulate labor with oxytocin./ to effect C/sec.

  • In practice, x-ray pelvimetry provides little help and in some cases may result in an increased and
    unnecessary C/sec rate.

1. Oxytocin stimulation

  • Exclusive criteria of contracted pelvis
  • Induction of labor

    • Stimulation of UC before the spontaneous onset of labor with/without ROM.
    • Elective induction of labor, defined as initiation of labor solely for convenience, is not recommended.

  • Augmentation

    • Stimulation of UC when spontaneous contraction have been considered inadequate, with failure to

2. Technique for IV oxytocin.

  • Risks vs Benefits of Oxytocin

    • Oxytocin : powerful drug --> leading to Uterine rupture & fetal death d/t hypoxia.
    • Failure to treat uterine dysfuction

      : maternal exhaustion, intrapartum infection & ttraumatic operative delivery.

      : increased perinatal morbidity & mortality.

VI. Amniotomy

  • AROM -- potential for infection, bleeding (from undiagnosed, placenta previa / low-lying placenta)

    -- Safe & decreased incidence of postterm gestation.

  • AROM : effective method of labor induction, esp. when the cervix is favorable.
  • Amiotomy for the purpose of hastening spontaneous labor has not proved effective.
  • Procedure : to avoid dislodging the fetal head, an assistant applying fundal & suprapubic pressure.

    --> reduce the risk of cord prolapse.

  • FHR should be assessed prior to and immediately after the procedure .

1. ROM without labor.

  • SROM without spontaneous UC : ca. 8% of term pregnancy.

  • Management : labor induction when labor did not commence after 6 ~ 12hr of observation.

    (because of maternal & fetal complication d/t amnionitis)

  • Observation of ROM without labor at term are very careful (d/t infection)

2. Prostaglandin.

  • for both cervical ripening & stimulation of labor
  • PG E2 used for cervical ripening rather than labor induction.

    (6% -- developed hyperstimulation)

3. Laminaria

(Synthetic hydroscopic cervical dilator)

- required about 10 devices to fill the endocervical canal.

4. Treatment of Hypertonic uterine dysfunction.

  • Hypertonic dysfuction

    • characterized by uterine pain.
    • occurs prior to the cervix reaching a dilatation of 4cm/more.
    • cf. relative infrequency --> little attention.
    • Placental abruptio must always be considered as a possible cause of uterine hypertonus.

      1. Oxytocin : rarely indicated.
      2. C/sec : if fetal distress (+)
      3. Sedatives (morphine / demerol) : if intact membrane & no evidence of CPD.

        --> relieve pain & rest the mother as well as arrest the abnormal uterine activity.
      4. Tocolytics.

    VII. Inadequate voluntary expulsive force

    1. Cause

    1. Conduction analgesia (lumbar epidural, caudal or intrathecal)
      : reduce the reflex urge for the woman to push, & impair her ability to contract the abdominal muscles
    2. General anesthesia.
    3. Long-standing paralysis of the abdominal musculature.

    2. Management.

    : careful selection of the kind of analgesia & the timing its administration.

    VIII. Localized abnormalities of uterine action.

    1. Pathologic retraction & contraction ring

    1. Pathologic contraction ring of Bandl

      • an exaggeration of the normal retraction ring. result of obstructed labor, with marked stretching &
        thinning of the lower uterine segment.

      • may be seen clearly as an abdominal indentation and signifies impending rupture of the lower uterine segment.

      • Localized constriction of uterus

        • hourglass constrictions of the uterus following the birth of the 1st of twins

          (Management -- relaxation, G/A, C/sec)

    IX. Precipitate labor & delivery

    • Result from an abnormally low resistance of the soft parts of the birth canal, from abnormally strong
      uterine & abdominal constriction, or very rarely, from the absence of painful sensation & thus a lack of
      awareness of vigorous labor.

    1. Maternal effect.

    • Seldom accompanied by serious complication.

      if the cervix : effaced appreciably &easily dilated, stretched vagina, relaxed perineum.

      if vigorous UC + long, firm cervix & vagina, vulva or perineum --> laceration of the cervix, vagina,
      vulva or perineum.

    • Amnionic fluid embolism.

    • Postpartum hemorrhage from placental implantation site.

    2. Fetal & neonatal effect

  • Perinatal mortality & morbidity inc.

    due to:
    1. tumultuous UC --> Uterine blood flow decreased --> fetal hypoxia.

    2. the resistance of the birth canal to expulsion of the head --> intraranial trauma.
    3. during an un attended birth --> fall down to the floor.

    3. Treatment.

    1. Analgesia : not likely to be modified to a significant degree.
    2. General anethesia.
    3. Stop oxytocic agent
    4. Tocolytics
    5. Indefensible to lock the mother's legs or hold the baby's head back directly in attempts to delay delivery --> may damage the infant's brain