Dystocia Due to Pelvic Contraction
Chapter 19 Dystocia Due to Pelvic Contraction
2. Fetal Presentation and Position
3. Course of Labor.
4. Maternal Effects
2) Uterine rupture
3) Fistula Formation
4) Intrapartum infection
5. Fetal Effects
1) Caput Succedaneum
2) Fetal head molding
3) Umbilical Cord Prolapse
6. Prognosis
7. Management
2. identification
3. prognosis
4. management
2) Radiological estimation -> not used.
3) Sonographic Measurements -> BPD &
HC
2. Estimation of Pelvic Capacity
2) X-ray pelvimetry
3) Indications for X-ray Pelvimetry
4) Hazards of Diagnostic Radiation
5) CT scanning
6) Technique
7) Advantages
8) Ultrasound : without immediate clinical
utility
9) MRI
10) Combined Ultrasound & X-ray Pelvimetry
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.
- face & shoulder presentations -> 3 times.
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
- ?nulliparity
- ?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)
- transverse (interspinous) - 10.5 cm
- Contracted midpelvis
- interischial spinous + posterior sagittal
diameters < 13.5 cm.
- interischial spinous diameter < 8 cm.
- interischial spinous + posterior sagittal
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.
- ?1st : to affect the subsequent management
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.
- ?maternal tissue thickness.
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.
- ?fetal head & AC using ultrasound.
- ?Maternal pelvic dimensions & fetal
AC were related to cesarean deliveries for fetopelvic disproportion
?(fetal HC was not identified as
a cause of dystocia).