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1. Cephalopelvic Disproportion
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2. Contents
• Definition
– CPD is failure of the fetus to pass safely through the birth canal because the fetal head being relatively larger
than the maternal pelvic size
– A disproportion in the size of the fetus relative to the maternal pelvis can result in failure to progress in the
second stage
• Common Causes
– fetal malposition
• extended or asynclitic fetal head, occiput posterior or transverse position
– Malpresentation
• mentum posterior, brow
• a true disparity between fetal size and maternal pelvic dimensions is rare
• However, true CPD may occur if
– fetus has a large surface anomaly (eg, teratoma, conjoined twin),
– maternal pelvic bone is very small or deformed (eg, after pelvic trauma), or
– fetus is extremely large (although vaginal deliveries have been described in infants weighing 13 to 17 pounds
and more).
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3. Diagnosis of CPD
• CPD is a subjective clinical assessment based on
– physical examination and
– course of labor (Trial of labor is best diagnostic tool)
• Antepartum, the clinician's ability to predict maternal pelvis-fetal size
discordance leading to arrest of labor requiring cesarean delivery has been
disappointing
– Clinical and radiologic assessments of the maternal pelvis and fetal size (ie, pelvimetry)
are inexact and poorly predict the course and outcome of labor
– Radiographic pelvimetry is not recommended
– Ultrasound evaluation of fetal position is accurate, but common malpositions such as
occiput posterior (OP) usually rotate intrapartum
• Suggestive findings - Intrapartum
– abnormal progress of labor
– physical findings: Progressive Caput & Molding
– protracted or arrested descent with increased molding, especially overlap of the parietal
bones at the sagittal suture, is suggestive of CPD
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4. Clinical Pelvimetry (👉👈)
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• Hip bone (os coxae)
– Sacrum, Ilium, Ischium
• Sacrum
– 5 fused bones
– Sacral promontory
• Coccyx
• Hip bones – 3 main articulations
– Sacroiliac joint
– Pubic symphysis
– Hip joint

5. 5

6. 6

7. Planes and Diameters of the Pelvis
• Pelvis - divided into
– False (lesser) pelvis: lies
above the linea
terminalis
• bounded posteriorly by
lumbar vertebra;
laterally by iliac fossa;
• Anteriorly by the lower
portion of the anterior
abdominal wall
– True: lies below the
linea terminalis
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8. Pelvic Joints
• Anteriorly - symphysis pubis
• limited degree of mobility
• During pregnancy, these joints relax remarkably at
term
– upward gliding of sacroiliac joint
• greatest in the dorsal lithotomy position
• may increase the diameter of the outlet by 1.5 - 2.0 cm for
delivery
– Sacroiliac joint mobility
• aids McRoberts maneuver to release an obstructed shoulder in
cases of shoulder dystocia
– These changes may also contribute to the success of the
modified squatting position to hasten SSOL
• squatting position may ↑ interspinous diameter & pelvic outlet
diameter
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9. 9

10. Estimation of Pelvic Capacity
• Clinically
– Inlet: Diagonal conjugate, prominence of sacral promontory
– Mid pelvis: Interspinous diameter
– Outlet:
• Subpubic angle (< 900 can signify a narrow pelvis)
• Intertuberous distances
• X-Ray Pelvimetry
• Computed Tomographic (CT) Scanning
• Magnetic Resonance (MR) Imaging
• In current obstetric practice
– Radiographic CT and MRI pelvimetry are rarely used
• lack of evidence of benefit
• some data that show possible harm
– Clinical pelvimetry
• the only method of assessing the shape and dimensions of the bony pelvis in labor
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11. • Pelvis is described as having four imaginary
planes
• greatest distance = transverse diameter = 13 cm
• clinically important: obstetrical conjugate
– shortest distance between the sacral promontory
and the symphysis pubis
– ≥ 10 cm, but unfortunately, it cannot be measured
directly
– So OC = DC – (1.5 to 2 cm)
Contracted Inlet
• Before labor, fetal BPD averages from 9.5 - 9.8
cm
• incidence of difficult deliveries rises when
– AP diameter of the inlet is <10 cm or
– transverse diameter is <12 cm
• inlet contraction usually is defined as a
diagonal conjugate <11.5 cm
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12. • measured at the level of the ischial spines
• smallest pelvic diameter = Interspinous diameter ≥ 10
cm
Contracted Midpelvis
• more common than inlet contraction
• Average midpelvis measurements
– Interischial spinous:10.5 cm
– AP (from lower border of symphysis pubis to the
junction of S4–5) = 11.5 cm
• No established definition of midpelvic contraction
– suspected whenever the interspinous diameter is
<10 cm
– When it measures < 8 cm, the midpelvis is
contracted
• Other suggestive features
– Prominent ischial spines
– pelvic sidewalls converge, or the sacrosciatic notch is
narrow
– narrowing of intertuberous diameter is a clue for
narrowing of the interspinous diameter
– A normal intertuberous diameter, however, does not
always exclude a narrow interspinous diameter
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13. • two approximately triangular areas
• Subpubic angle = ≥ 90 to 100 degrees
• Unless there is significant pelvic bony
disease, the pelvic outlet seldom obstructs
vaginal delivery
Contracted Outlet (Rare ~ 1%)
• usually is defined as an interischial tuberous
diameter of ≤ 8 cm
• Outlet contraction without concomitant
midplane contraction is rare.
• Although the disproportion between the fetal
head and the pelvic outlet is not sufficiently
great to give rise to severe dystocia, it may play
an important part in perineal tears
• of no obstetrical significance
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• Any contraction of the pelvic diameters that diminishes
pelvic capacity can create dystocia during labor

14. Grossly contracted pelvic if
o True conjugate is < 10 cm
o bituberous diameter of < 8 cm
• Other suggestive pelvic findings
– prominent ischial spine
– diverging pelvic walls
– flat sacrum
– narrow sacrosciatic notch
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Critical limit values are measurements

15. Pelvic Shapes
• Caldwell–Moloy (1933, 1934) anatomical
classification of the pelvis is based on shape
1. Gynecoid = found in 50% of females
– classic female shape
2. Anthropoid
– exaggerated oval shape of the inlet, largest AP
diameter, and limited anterior capacity
– more often associated with delivery in OP
position
3. Android = male
– increased risk of CPD
4. Platypelloid
– theoretically predisposes to a transverse arrest
Q: A pelvis characterized by an anteroposterior
diameter of the inlet greater than the transverse
diameter is classified as
a. Gynecoid b.Android
c.Anthropoid d. Platypelloid
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16. 16

17. Clinical classification
1. Absolute CPD
– true mechanical obstruction as a result of
– Permanent (maternal factors): contracted pelvis
(commonest), pelvic exostoses, spondylolisthesis,
anterior sacrococcygeal tumors or
– Temporary (fetal factors): Hydrocephalus, Large
infant
2. Relative CPD
– where the fetus may be delivered vaginally if a
favorable combination of other factors can be
achieved
– Example: brow presentation, face presentation and
occipito-posterior positions (rotation / flexion of
the head may occur during labor progress)
1. Suspect CPD
– Previous prolonged labor with bad obstetric
history or operative delivery
– Primigravida especially if age is less than 16 years
– True conjugate of 8 – 10 cm (borderline CPD)
– Prominent ischial spines, flat sacrum etc
– The cervicogram crossing the alert line without
signs of CPD (see section on abnormal labor)
2. Gross CPD
– Estimated fetal weight of 4 or more kg (in an
average sized Ethiopian)
– Hydrocephalus
– Gross traumatic or congenital pelvic abnormality
– True (obstetric) conjugate and/ or bituberous
diameter of less than 8 cm
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18. Diagnostic approach and risk assessment
• Diagnosis of CPD in the absence of gross CPD is confirmed
after trial of labor:
– Severe molding at a higher station (3/5th or more above the pelvic
prim);
– Increasing molding with no progress in descent
– Secondary arrest of cervical dilation and descent with good
contraction;
– In the primigravida, failure of progress of labor after augmentation
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19. Antepartum evaluation
• Clinical pelvimetry
• EFW (Sonography)
Intrapartum evaluation
• CPD, with very few exceptions, is diagnosed after a properly conducted trial of labor
• Abdominal and pelvic assessment should be done in all laboring mothers to rule out CPD
• Findings that may indicate CPD are
– Abnormal progress of labor
– Abnormal clinical pelvimetry
– Molding
– Caput Succedaneum – due to prolonged labor and CPD
• Severe degree of caput is diagnosed when the scalp oedema hampers identification and assessment of the
suture lines
– Abnormal degree of head flexion (deflexion)
– Fetal distress
– Asynclitism
– Fetal Macrosomia
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20. Trial of labor
• conducted in a woman with suspected CPD to determine whether it is
safe for the woman to deliver vaginally or not
• in an equipped and staffed hospital for operative procedures in case vaginal
delivery fails.
• CPD is suspected if
– previous history of prolonged labor with bad obstetric history or operative
delivery
– parturient is teenage
– borderline pelvis: obstetric conjugate is 8 to 10 cm
– cervicogram is crossing the alert line without signs of CPD.
• The trial continues as long as labor progresses well and as long as there is
reassuring fetal and maternal status.
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21. Modified Mueller-Hillis Maneuver
• performed in the late active phase of the first stage of labor
• For predicting abnormalities in second stage labor
• positive modified Mueller-Hillis maneuver in second stage labor
– Definition: descent of the fetal head of > 1cm with fundal pressure
– had a high predictive value for vaginal delivery
• Negative maneuver
– was significantly associated with high operative delivery rate, prolonged second
stage labor and abnormal position
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22. Fetal pelvic index (FPI) to predict CPD
• Calculated based on on the basis of four circumference differences between the fetus and
the maternal pelvis by subtracting the maternal pelvic inlet and midpelvic circumferences
(IC and MC, respectively) from the fetal HC and AC
– (HC–IC, HC–MC,AC–IC,AC–MC)
• An index value was derived by adding the two most positive circumference differences
• FPI = (HC–IC) + (HC–MC) + (AC–IC) + (AC–MC)
• IC: pelvic inlet circumference
• MC: midpelvic circumference
– Positive FPI (cut-off zero): fetuses larger than the maternal pelvis
– Negative FPI: fetuses smaller than the maternal pelvis
• not a clinically useful tool to predict the mode of delivery for patients at high risk of
cephalopelvic disproportion
• The pooled analysis of the current and previous studies strengthened this conclusion
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23. Route of delivery
• CS
– Gross CPD during labor
– In permanent absolute disparities
• severe pelvic contracture (OC of 6 - 8 cm) or
• extreme pelvic contracture (OC < 6 cm)
– Macrosomia
• > 4.5 kg (IDM) or > 5 kg for non diabetic infant
• Avoid Induction and augmentation in fetal macrosomia
• Fetal hydrocephalus may be managed by Cephalocentesis
• Craniotomy is indicated if the fetus is dead and prerequisites for
destructive delivery are fulfilled.
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24. Treatment plan
• CS for gross CPD with normal fetus
– Hydrocephalus is managed by craniocentesis
– If gross CPD with normal fetus is diagnosed, elective CS is appropriate
• Suspected CPD:
– Plan place of delivery at a hospital (where CS service is available) or health
center with timely referral service to a hospital.
– Conduct trial of labor using Partogram
– Emergency CS is done when CPD is diagnosed after trial of labor
• Obstructed labor or ruptured uterus
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25. Complications
• Maternal
– Prolonged / obstructed labor: If CPD is not
diagnosed & properly managed the end
result is obstructed labor and its
associated complications.
– PPH
– Maternal sepsis
• Fetal / neonatal
– Fetal distress
– Perinatal asphyxia
– Neonatal infections
– Perinatal death
Discharge counselling & education
• A woman who delivered by CS should
be explained about the indication
(CPD) and the need for repeat CS in
future pregnancy
• Besides verbal explanation, a written
note should be given that could also
serve as referral feedback to referring
health centers
• Previous CS for CPD can be followed
at a nearby health center and referred
after 36 - 37 weeks of gestation
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26. Common Q & As
Bones forming pelvis: Innominate, Sacrum, Coccyx
Clinical evaluation of the pelvic inlet: Diagonal conjugate
Shortest anteroposterior diameter of the pelvic inlet: Obstetrical
conjugate
regarding relaxation of the pelvic joints at term in pregnancy
– Displacement of the SI joint increases outlet diameters by 1.5 to 2.0
cm in the dorsal lithotomy position.
Midpelvis - is measured at the level of the ischial spines
the narrowest pelvic dimension that must be navigated by the fetal head:
Interspinous diameter
The pubococcygeus muscle is now preferably called which of the following?
– Pubovisceral muscle
The posterior triangle of the pelvic outlet is limited at its apex by which of
the following?
– A. Coccyx B. Last sacral vertebrae C. S4 D. S3
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