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Dystocia Due to Pelvic Contraction

Chapter 19 Dystocia Due to Pelvic Contraction


1st year resident, Lee Sun Joo

I. Contracted Pelvic Inlet

1. definition

  • ?shortest AP diameter < 10.0 cm or
    greatest transverse diameter < 12.0 cm.

  • ?AP diameter : commonly approximated
    by manually measuring the diagonal conjugate, which is about 1.5cm greater.

  • ?Inlet contraction : diagonal conjugate
    < 11.5cm.

  • ?Prior to labor, the fetal BPD has been
    shown to average from 9.5 to as much as 9.8cm in different populations.


  • ?The configuration of the pelvic inlet
    is also an important determinant of the adequacy of any pelvis.


  • ?A small woman : have a small pelvis
    & small infant.


  • ?In most species maternal size rather
    than paternal size is the important of fetal size.


2. Fetal Presentation and Position
  • ?A contracted inlet plays an important
    part in the production of abnormal presentations.


  • ?Contracted inlet -> descent usually
    does not take place until after the onset of labor, if at all.


  • ?In women with contracted pelves :
    • face & shoulder presentations -> 3 times.
    • cord prolapse -> 4 to 6 times more frequently.


3. Course of Labor.
  • ?Severe pelvic deformity -> labor is
    prolonged & effective spontaneous labor is often never achieved.


4. Maternal Effects

1) Abnormalities in Cervical Dilatation

  • ?When the head is arrested in the pelvic
    inlet the entire force acts directly upon the portion of membranes that
    overlie the dilating cervix.? ->?? Early ROM is more likely
    to result.


  • ?After membrane rupture, further dilatation
    may proceed very slowly or not at all.


  • ?Cervical response to labor provides
    a prognostic view of the outcome of labor.


2) Uterine rupture
  • ?CPD is so pronounced that there is no
    engagement & descent -> the lower uterine segmetn rupture may follow.


  • ?Pathological retraction ring -> immediate
    abdominal delivery is indicated.


3) Fistula Formation
  • ?Pelvic wall -> because of impaired circulation,
    necrosis may result -> vesicovaginal, vesicocervical, rectovaginal fistulas.

  • ?Pressure necrosis follows a very prolonged
    2nd stage of labor.


4) Intrapartum infection
  • ?by prolonged membrane rupture

  • ?by repeated cervical examinations &
    intrauterine manipulations.


5. Fetal Effects
  • ?contracted pelvis -> prolonged ROM &
    intrauterine infection? -> fetal & maternal risks are compounded.


1) Caput Succedaneum
  • ?contracted pelvis -> a large caput succedaneum
    develops on the most dependent part of the fetal head.


  • ?may assume considerable size & lead
    to serious diagnostic errors.


2) Fetal head molding
  • ?molding -> cranial plates overlapping
    one another at the major sutures.


  • ?frequently accomplished without obvious
    detriment.


  • ?may lead to tentorial tears, laceration
    of fetal blood vessels and fatal intracranial hemorrhage.


  • ?molding was greatest in the suboccipito
    bregmatic dimension & averaged 0.3cm with a range up to 1.5cm(The BPD
    was not affected).


  • ?Factors associated with molding

    • ?nulliparity
    • ?oxytocin labor stimulation
    • ?delivery with a vacuum extractor

  • ?locking mechanism -> protection for
    the fetal brain.


  • ?characteristic pressure marks?
    -> covering the portion of the head that passes over the promontory of
    the sacrum.


  • ?skull fractures -> usually following
    forcible attempts at delivery may occur with spontaneous delivery or even
    with cesarean delivery.


3) Umbilical Cord Prolapse
  • ?facilitated by imperfect adaptation
    between the presenting part and the pelvic inlet.



    ¡§c rapid filling of the urinary
    bladder with 500 to 700ml of normal saline.


    ¡§e intravenous ritodrine prior
    to cesarean delivery.

6. Prognosis
  • ?AP diameter of less than 9cm.?
    -> successful vaginal delivery of a term-sized fetus is nearly hopeless.


  • ?slightly below 10cm -> the prognosis
    for vaginal delivery.



    ¡§c presentation : all presentations
    but the occiput are unfavorable.


    ¡§e fetal size is of obvious
    importance.


    ¡§e pelvic inlet diameters &
    configuration.


    ¡§e The frequency and intensity
    of uterine contractions are informative.


    ??? --> uterine dysfunction
    is common with significant disproportion.


    ¡§e cervical response to labor.

    ¡§i Extreme asynclitism &
    appreciable molding of the fetal head without engagement.


    ¡§i Previous labor and delivery
    outcomes at term previous infant weights.


    ¡§i Coincidental conditions that
    impair uteroplacental perfusion.

7. Management
  • ?A delivery that is safe for both mother
    and child cannot be anticipated.


  • ?Inlet contractions : weak uterine contractions
    during 1st-stage labor and a need for vigorous voluntary expulsive efforts
    during the 2nd stage.




II. Contracted Midpelvis

1. definition

  • ?midpelvis : inferior margin of the symphysis
    pubis? ¢®¡© ischial spines ¢®¡© sacrum near the junction
    of the 4th & 5th vertebrae.

  • ?A transverse line (connecting the ischial
    spines)?? -> divides the midpelvis into anterior & posterior
    portions.


  • ?Anterior : lower border of the symphysis
    pubis ¢®¡© ischiopubic rami.



    ?Posterior : sacrum ¢®¡©
    sacrospinous ligaments.

  • Average midpelvis measurements

    • transverse (interspinous) - 10.5 cm

    • anteroposterior??????????
      - 11.5 cm


    • posterior sagittal????????
      -? 5 cm


    ?????????
    (from the midpoint of the interspinous line to the same point on the sacrum)

  • Contracted midpelvis

    • interischial spinous + posterior sagittal
      diameters < 13.5 cm.


    • interischial spinous diameter < 8 cm.


2. identification
  • ?the spines are prominent.

  • ?the pelvic side walls converge.

  • ?the sacrosciatic notch is narrow.

3. prognosis
  • ?more common than inlet contraction.

  • ?a cause of transverse arrest of the
    fetal head.


4. management

  • ?perineum is bulging & vertex is
    visible -> the head has passed the obstruction.


  • ?strong fundal pressure should not be
    used.


  • ?vacuum extractor -> be of advantage
    after the cervix had become fully dilate



    ? -> should not be applied unless
    the BPD has passed the??? pelvic obstruction.



III. Contracted Pelvic Outlet

1. definition & incidence

  • ?diminution of the interischial tuberous
    diameter < 8cm.


  • ?anterior triangle : pubic rami. ¢®¡©
    inferior posterior surface of the symphysis pubis.



    ?posterior triangle : tip of the
    last sacral vertebra.









2. prognosis

  • ?delivery -> partly depends on the size
    of the posterior triangle, or more on the interischial tuberous diameter
    and the posterior sagittal diameter of the outlet.


  • ?outlet contraction with concomittant
    midplane contraction.


  • ?the disproportion between the fetal
    head & the pelvic outlet



    ?-> the production of perineal tears.



IV. Pelvic Fractures and Pregnancy

?

  • ?careful review of previous X-rays &
    possibly CT pelvimetry later in pregnancy.




V. Rare Pelvic Contractions.

?

  • ?dwarfs, poliomyelitis, Kyphoscoliosis,
    small & dysmorphic women



    ?? -> cesarean delivery.



VI. Estimating Fetal Head Size & Pelvic Capacity.

1. fetal head size

1) clinical estimation

  • ?fundal pressure -> If no disproportion
    exists, the head readily enters the pelvis? -> vaginal delivery.


  • ?A flexed fetal head that overrides the
    symphysis pubis -> presumptive evidence of disproportion.


  • ?No relation between dystocia & failure
    of descent of the head.


2) Radiological estimation -> not used.

3) Sonographic Measurements -> BPD &
HC

  • ?freely floating fetal head -> invalidate
    the measurement.


  • ?dolichocephlic (elongated in the occipito
    frontal diameter)



    ?? -> underestimate fetal weight
    & gestational age


    ?? -> HC measurement is more
    accurate.

2. Estimation of Pelvic Capacity

1) clinical estimation


  • Anteroposterior diameter of the inlet.

  • ?the interspinous diameter of the midpelvis

  • ?the intertuberous distances of the pelvic
    outlet.


  • ?A narrow pelvic arch(< 90 degrees
    ) -> narrow pelvis.


2) X-ray pelvimetry
  • ?5 factors of successful vaginal delivery.


    ¡§c size & shape of the
    bony pelvis.


    ¡§e size of the fetal head.

    ¡§e force of the uterine contractions.

    ¡§e moldability of the fetal
    head.


    ¡§e presentation & position
    of the fetus.

  • ?Cephalic fetal presentation -> not necessary

        ???????????????????????????
        -> X-ray pelvimetry still is used(in breech).



3) Indications for X-ray Pelvimetry
  • ?The women with a previous injury or
    disease likely to affect the bony pelvis.


  • ?essential questions

    • ?1st : to affect the subsequent management
      of labor & delivery.


    • ?2nd : are other types of imaging techniques
      available for pelvimetry measurements.



4) Hazards of Diagnostic Radiation
  • ?The possibility of childhood malignancy
    was raised.


  • ?increased morbidity & martality
    have not been identified.


5) CT scanning
  • ?2 digital radiographs (AP & lateral
    views)


  • ? -> sufficient to measure the necessary
    pelvic diameters including the? interspinous.


  • ?fetal exposure :

    • ?maternal tissue thickness.

    • ?fetal size & position,

    • ?distance from the radiation source.

    • ?time of exposure.


6) Technique
  • ?AP view -> Electronic calipers are used
    to measure the transverse diameter of the inlet.


  • ?Lateral view -> AP diameter of the inlet
    & mid-pelvis.


  • ?At the center of the table.

  • ?Maternal movement is kept at a minimum.

  • ?Interspinous diameter -> an axial section
    through the fovea of the temoral heads.


7) Advantages
  • ?reduction in radiation exposure.

  • ?the greater accuracy.

  • ?easier to perform.

8) Ultrasound : without immediate clinical
utility


9) MRI
  • ?lack of ionizing radiation

  • ?accurate pelvic measurements.

  • ?complete fetal imaging.

  • ?the potential for evaluating reasons
    for soft tissue dystocia.


  • ?expense, time, availability of equipment.

10) Combined Ultrasound & X-ray Pelvimetry
  • ?Fetal-pelvic index

    • ?fetal head & AC using ultrasound.

    • ?maternal pelvic inlet & midpelvic
      circumferences using X-ray pelvimetry.



  • ?Maternal pelvic dimensions & fetal
    AC were related to cesarean deliveries for fetopelvic disproportion



    ?(fetal HC was not identified as
    a cause of dystocia).