Dystocia caused by pelvic contraction

Chapter 19. Dystocia caused by pelvic contraction

July 1, 1996 , 1st year resident J.W. Lee. M.D.

# Classification

  1. Contraction of the Pelvic inlet
  2. Contraction of the Midpelvis
  3. Contraction of the Pelvic outlet
  4. Generally contracted pelvis (Combinations of the above)

A. Contraction of the Pelvic inlet

1. Definition

  • Shortest A-P dia : < 10cm, D.C < 11.5cm or

  • Greatest transverse dia. < 12cm

    Normal fetal BPD : 9.5 ~ 9.8cm

    Both dia. are contracted --> obstetric difficult inc.

  • Defined as a diagonal conjugate of less than 11.5cm

    # Configuration of inlet : also important determinant

    # Small women is likely to have a small pelvis, and she is more likely to have small infant.

    # Maternal size rather than paternal size is the important determinant of fetal size.

2. Size of the fetal head

(1) Clinical estimation

(2) Radiologic estimation

(3) Sonographic measurement

  • in breech presentation (free floating head)

    -- invalid due to

    (1) move sufficiently &

    (2) dolichocephaly <-- multifetal gestation, oligohydramnios.

    : measure head circumference rather than BPD.

  • Fetal - pelvic index
  • Standardized method for comparing fetal size with the respective maternal pelvis
  • Fetal head & abd. circumference by USG
  • Maternal pelvic inlet & midpelvic circumference by X-ray pelvimetry
  • " Fetal - pelvic index " number based upon differences in the pelvis & fetal circumference.
  • Maternal pelvic dimensions & fetal abd. circumference were related to C/S for CPD.

    c.f.) Fetal head circumference was not identified as a cause of dystocia.

3. Presentation & position of the fetus

  • Contracted pelvic inlet play an important part in the production of abnormal presentation

    ex) In women with contracted pelvis.

    Face & shoulder presentation : *3 inc

    Prolapse of the cord and of the extremity : * 4~ 6 inc

4. Course of labor

  • Course of labor is prolonged, often, effective labor is never achieved.

    --> result in serious maternal & fetal effects.

5. Maternal effect

1) Abnormalities in dilatation of the cervix

  • Normally, at unrupture membrane, hydrostatic action --> facilitated cervical dilatation.
    after rupture, by direct application of the P.P. against the cervix.

  • Contracted pelvis --> early SROM
    --> absence of pressure by fetal head against the cervix & lower ut. segment.

    --> less effective ut. contraction

    --> cervical dilatation may proceed very slowly or not at all

  • Cervical response to labor provides a prognostic view of the outcome of labor in women with inlet

2) Danger of Uterine rupture

  • Pathologic retraction ring

    : felt as a transverse or oblique ridge extending across the uterus somewhere between the
    symphysis & the umbilicus.

    : danger of ut. rupture --> prompt delivery or C/S

3) Production of fistula

    P.P dose not advance --> excessive pressure to pelvic wall --> impaired circulation

    -->necrosis --> vesicovaginal, vesicocervical, rectovaginal fistula formation.

4) Intrapartum infection

    increased by :

    # 1. Prolonged ROM ,

    # 2. Frequent vaginal exam.

    # 3. Intraut. manipulation.

    If the amnionic fluid becomes infected, fever may or may not develop during labor.

6. Fetal effects

  • Prolonged labor in itself may be deleterious to the fetus.
  • Perinatal mortality rate inc (labor > 20hr, 2nd stage > 3hr)
  • Abnormal labor (labor disorder) : not a/w neurological morbidity.
  • Nenatal IQs ?
  • Intrapartum infection : serious maternal complication and important cause of fetal & neonatal death.
  • Bacteria in amnionic fluid --> transverse the amnion --> invade decidua & chorionic vessels.

    --> maternal & fetal bacteremia.
  • Fetal pneumonia. ; caused by aspiration of infected amnionic fluid.

    1) Caput succedaneum formation

    • most dependent part of the head

    • the caput may reach almost to the pelvic floor while the head is still not engaged

      --> an inexperienced physician may make premature & unwise attempts at forceps delivery

    • the large caput disappears within a few days after birth

    2) Molding of the fetal head

    • the bone of the skull overlap one another at the major suture

      As a rule, median margin of the parietal & frontal bone is overlapped.

      c.f.) occipital bone is pushed under the parietal bone.

    • When distortion is marked

      --> tentorial tears, laceration of fetal blood vessels, and fetal ICH.

    • Diminution of 0.5cm or more in the BPD

      cf. greatest in the suboccipitobregmatic dimension (0.3 ~ 1.5cm)

      Factors a/w molding

      # 1. Nulliparity

      # 2. Oxytocin stimulation

      # 3. Vacuum extractor

    • Head is softer and readily molded --> spotaneous delivery.

      c.f.) more ossified head --> require operative delivery.

      fracture of the skull are often encountered

      : 2 varieties

      #1 Shallow groove -- not very dangerous

      #2 Spoon-shaped depression just post. to the coronal suture --> may lead to death.

    3) Prolapse of the cord

    • Facillitated by imperfect adaptation between the P.P. & pelvic inlet.
    • Mx.

      # 1. Prompt delivery

      # 2. Rapid filling of bladder with 500 ~ 700cc of N/S --> elevate the P.P.

      # 3. IV ritodrine (uterine relaxation prior to C/S)

7. Prognosis

  • A-P dia. < 9cm -- nearly hopeless

    Borderline -- slightly below 10cm

  • Variable factors for successful vaginal delivery

    1. Presentation : all presentation but the occiput are unfavorable
    2. Fetal size
    3. Dia. & configulation of the pelvic inlet
    4. the Frequency and intensity of spontaneous uterine contraction.
    5. Behavior of the cervix
    6. Extreme asynclitism is unfavorable
    7. Knowledge of the outcome of previous labor and delivery at term.
    8. Coincidental conditions.

8. Treatment

A. Carefully managed trial of labor

  • Caution : use of conduction analgesia with greater parity, uterine rupture inc.

B. C/S

C. Administration of oxytocin --> should be avoided.

B. Contracted Midpelvis

1. Definition

  1. Interischial spinous dia. + Post. sagital dia. < 13.5cm ( Normal : 15.5 ~ 16cm )
  2. Interischial spinous dia. < 9cm

    Interischial spinous dia. <10cm : suspect

2. Identification

  • No precise manual method of ascertaining midpelvic contraction
  • Suggestion by pelvic exam.

    1) the spines are prominent

    2) the pelvic sidewalls converge

    3) the sacrosciatic notch is narrow

    4) the intertuberous dia. is narrow

3. Prognosis

  • more common than inlet contraction
  • frequently a cause of transverse arrest of fetal head.

4. Treatment

1) Midforceps delivery

  • C/Ix : BPD has not passed beyond the level of contraction

2) Vacuum extractor : advantage in some cases

  • as with forceps, the vacuum extractor should not be applied unless the BPD has passed the pelvic obstruction.

3) Oytocin : contraindicated

C. Contracted pelvic outlet.

1. Definition & Incidence

  • Interischial tuberous dia. < 8cm
  • Incidence : 0.9%

2. Prognosis

  • Outlet contraction without concomitant midplane is rare
  • Interischial tuberous dia.& the PSD are important.
  • may play an important part in the production of perineal tears
  • extensive mediolateral episiotomy is usually indicated

D. Generally contracted pelvis

E. Pelvic fracture and pregnancy

  • Common cause : automobile collisions
  • Callus formation or malunion was very common
  • History of previous X-rays and radiologic evaluation.

    # rare pelvic contraction

# Kyphotic pelvis

  1. Diagnosis
      : obvious, external deformity is visible, peudoconjugate

  2. Effect upon labor
      : the ischial tuberosities < 8cm : difficult or impossible

  3. Effect upon heart
      : heart failure

  4. Prognosis & Treatment

    • Thoracic : cardiac complication
    • Lumbar : midpelvic contraction
    • Lower : contraction may be extreme
    • C/S