What is the best approach for a pregnant individual suspected of having cephalopelvic disproportion (CPD)?

Management of Suspected Cephalopelvic Disproportion

When cephalopelvic disproportion (CPD) is suspected or cannot be ruled out with reasonable certainty, cesarean delivery is the safest and most prudent option to prevent maternal and fetal harm. 1, 2

Initial Assessment and Diagnosis

Clinical Evaluation for CPD

The diagnosis of CPD requires a thorough cefalopelvimetric evaluation focusing on specific clinical signs 1, 2:

• Serial suprapubic palpation of the base of the fetal skull is essential to differentiate true descent from molding alone—this is the most critical examination technique 1, 2
• Look for increasingly marked molding, deflexion, and asynclitism of the fetal head without actual descent despite contractions 2
• CPD occurs in 40-50% of all active phase arrest cases and 25-30% of cases with active phase disorders, making it a primary consideration in labor abnormalities 1, 2

Risk Factors to Identify

Maternal factors associated with CPD include 1, 2:

• Maternal diabetes 1, 2
• Maternal obesity 1, 2

Fetal factors include 1, 2:

• Macrosomia 1, 2
• Malposition (occiput posterior or transverse) 2
• Malpresentation (such as brow presentation) 2
• Marked asynclitism 2
• Excessive molding without descent 2

Objective Measurements (When Available)

• Fetal head circumference ≥34.8 cm has 88% sensitivity and 74% specificity for predicting CPD requiring cesarean section 1
• Ultrasound pelvimetry combined with fetal biometry can be performed: the cephalopelvic index of diameter (CID), defined as the difference between mean diameter of the midpelvis and fetal biparietal diameter, with CID <15.8 mm predicting 83% operative delivery rate 3
• Transvaginal ultrasound pelvimetry is quick, painless, and allows measurement of both true conjugate and transverse diameter of the pelvic inlet 4

Management Algorithm

When CPD is Confirmed or Cannot be Ruled Out

Proceed directly to cesarean delivery 1, 2:

• The American College of Obstetricians and Gynecologists explicitly states: "it is better to err on the side of intervention by cesarean delivery in the presence of uncertainty about potential harm than to allow labor in the false hope that safe vaginal delivery may occur" 2
• The risks of maternal and fetal damage are too great to attempt vaginal delivery when CPD is present or cannot be excluded with reasonable certainty 1, 2

Critical Contraindications When CPD is Present

Oxytocin augmentation is absolutely contraindicated 1, 2:

• Attempting oxytocin in the presence of CPD risks uterine hyperstimulation, uterine rupture, severe maternal lacerations, excessive fetal molding, and potential asphyxia without achieving vaginal delivery 2
• Ecbolic agents are best avoided when associated with evidence of CPD 2

Artificial rupture of membranes has no objective evidence of benefit for arrest of dilation and should not be performed 1

Operative vaginal delivery should not be attempted when CPD is confirmed—a complete cefalopelvimetric evaluation is crucial before considering any operative vaginal delivery, and CPD represents a clear contraindication 1

When CPD is Definitively Ruled Out

If after thorough evaluation CPD can be confidently excluded 1:

• Vaginal delivery is preferable, provided it does not prove difficult 1
• Standard labor management protocols may be followed 1

Special Populations

Women with Skeletal Dysplasia

Cesarean delivery is recommended as the standard approach 5, 1:

• Pelvic anatomy in most women with skeletal dysplasia precludes vaginal delivery 5, 1
• The infant's cranium will be too large to pass through the birth canal whether the infant has average stature with normocephaly or short stature with macrocephaly 5
• Aside from rare cases of adequately sized pelvis in mild hypochondroplasia, cesarean delivery is necessary 5
• A Pfannenstiel skin incision and low transverse uterine incision can be used 5

Timing Considerations

Astute clinicians will often recognize CPD and proceed to cesarean delivery before formal arrest criteria are met, especially when malposition or excessive molding is noted on examination 2. Early recognition and intervention prevent prolonged labor with its associated complications 6.

Common Pitfalls to Avoid

• Do not continue labor with instructions to push when CPD is suspected—this is futile and dangerous 1
• Do not delay referral in resource-limited settings: early referral before advanced cervical dilation (especially before 10 cm) improves outcomes, particularly in obese women and complicated pregnancies 6
• Do not confuse molding with actual descent—serial suprapubic palpation of the skull base is the only reliable method to distinguish these 1, 2
• Do not wait for Category III fetal heart rate patterns to make the decision for cesarean delivery when CPD is evident 2