What is the management approach for a pregnant woman at 36-38 weeks of gestation with suspected cephalopelvic disproportion (CPD) during antenatal assessment?

Management of Suspected Cephalopelvic Disproportion at 36-38 Weeks

When cephalopelvic disproportion (CPD) is confirmed or cannot be ruled out with reasonable certainty at 36-38 weeks gestation, proceed directly to planned cesarean delivery—this is the safest and most prudent option to prevent maternal and fetal harm. 1, 2

Antenatal Assessment Components

General Examination - Maternal Risk Factors

Identify maternal factors that increase CPD risk:

• Maternal diabetes and obesity are strongly associated with CPD 1, 2
• Maternal head circumference relative to height (head circumference in cm divided by height in meters) is a significant predictor—larger ratios increase CPD risk 3
• Maternal height, foot length ≤23 cm, and inter-trochanteric diameter ≤30 cm are anthropometric predictors of CPD 4

Fetal Assessment

Evaluate fetal factors associated with CPD:

• Macrosomia (estimated fetal weight ≥3,000g) is a key risk factor 1, 2, 4
• Fetal head circumference ≥34.8 cm has 88% sensitivity and 74% specificity for predicting CPD requiring cesarean section 2, 5
• Fetal malposition, malpresentation, and marked asynclitism increase CPD risk 2

Pelvic Assessment

Serial suprapubic palpation of the base of the fetal skull is the most critical examination technique to differentiate true descent from molding alone 1, 2. This is essential because molding without actual descent indicates mechanical obstruction.

Advanced imaging considerations (though not routinely available):

• The mid-pelvic cephalopelvic circumference index (MP-CPCI), calculated as fetal head circumference/pelvic circumference × 100, shows that each 1% increase raises CD risk by 11% 6
• MP-CPCI ≥110 dramatically increases CPD risk (adjusted OR 21.44) 6
• The cephalopelvic index of diameter (CID), defined as mean midpelvic diameter minus fetal biparietal diameter, shows 83% of cases with CID <15.8 mm require operative delivery 7

Management Algorithm

When CPD is Confirmed or Cannot Be Ruled Out:

1. Schedule planned cesarean delivery immediately 1, 2
2. Oxytocin augmentation is absolutely contraindicated—it risks uterine hyperstimulation, uterine rupture, severe maternal lacerations, excessive fetal molding, and potential asphyxia without achieving vaginal delivery 1, 2
3. Do not attempt operative vaginal delivery—CPD represents a clear contraindication 2
4. Artificial rupture of membranes has no objective evidence of benefit for labor arrest and should not be used 1

When CPD is Definitively Ruled Out:

If comprehensive cefalopelvimetric evaluation excludes CPD with reasonable certainty, vaginal delivery is preferable provided it does not prove difficult 1

Critical Clinical Context

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 when labor abnormalities are present 2. However, the provided evidence acknowledges that current diagnostic methods for CPD remain imperfect—advanced 3D/4D sonography and other imaging techniques to assess spatial relationships between fetal skull and maternal pelvis are still under investigation 8.

Special Populations

Women with skeletal dysplasia require cesarean delivery as the standard approach, as pelvic anatomy typically precludes vaginal delivery regardless of infant size 1, 2

Common Pitfalls to Avoid

• Do not continue labor with oxytocin when CPD cannot be excluded—the risks of maternal and fetal damage are too great to attempt vaginal delivery when CPD is likely 1, 2
• Do not rely solely on clinical pelvimetry—it has limited accuracy; serial suprapubic palpation assessing actual fetal descent (not just molding) is more reliable 1, 2
• Do not delay decision-making—at 36-38 weeks with suspected CPD, plan for cesarean delivery rather than waiting for a trial of labor that may result in emergency cesarean with worse maternal outcomes 2