What are the treatment options for a patient with pelvic inlet contraction?

Management of Pelvic Inlet Contraction

The primary treatment decision for pelvic inlet contraction hinges on thorough cephalopelvimetry to exclude cephalopelvic disproportion (CPD), followed by either cesarean delivery when CPD is confirmed or a trial of labor with careful oxytocin augmentation when CPD is ruled out. 1

Initial Assessment and Risk Stratification

When pelvic inlet contraction is suspected, the evaluation must focus on identifying CPD, which occurs in 25-30% of cases with labor abnormalities and in 40-50% of women with arrested active phase labor. 1 The clinical examination should specifically assess for:

• Increasingly marked molding of the fetal head 1
• Deflexion or asynclitism without descent 1
• Fetal macrosomia, hydrocephalus, or malposition (occiput posterior/transverse) 1
• Maternal obesity and advanced age 1

Treatment Algorithm Based on CPD Status

When CPD is Confirmed or Suspected

Proceed directly to cesarean delivery rather than attempting vaginal delivery, as it is better to err on the side of intervention than to allow labor in false hope of safe vaginal delivery. 1 This recommendation is particularly critical because:

• The potential risks associated with CPD outweigh the benefits of attempting vaginal delivery 1
• Astute clinicians should recognize problems before formal arrest criteria are met, especially with malposition or excessive molding 1
• Oxytocin augmentation is contraindicated when CPD is present 1

When CPD is Ruled Out

If thorough cephalopelvimetry excludes CPD, vaginal delivery becomes preferable with the following management approach: 1

Careful oxytocin augmentation can be initiated with these specific parameters:

• Titrate infusion rate slowly in small increments according to uterine response 1
• Monitor for uterine hyperstimulation risk 1
• Expect progress within 2-4 hours (recent evidence suggests 2 hours is safer, though 4 hours may be acceptable) 1

Monitoring for treatment response:

• A good response shows effective contractions with progress in cervical dilatation, signaling good prognosis for safe vaginal delivery 1
• If the post-arrest slope of dilatation improves over the pre-arrest slope, chances of harm-free vaginal delivery increase 1
• If no dilatation occurs after oxytocin therapy, proceed to cesarean delivery as the safer option 1

Critical Decision Points During Labor

When to Abandon Trial of Labor

Convert to cesarean delivery immediately if: 1

• No progress in dilatation occurs despite oxytocin augmentation
• Evidence of CPD emerges during labor (marked molding, deflexion, asynclitism without descent)
• The post-arrest dilatation rate does not improve over the pre-arrest rate

Interventions to Avoid

Artificial rupture of membranes has no objective proof of usefulness for protraction or arrest of dilatation in the context of pelvic inlet contraction. 1 It should only be performed when there is an overriding reason, such as applying fetal monitoring scalp electrodes or inserting an intrauterine pressure transducer. 1 If a response occurs, it will happen promptly. 1

Common Pitfalls and How to Avoid Them

• Do not delay cesarean delivery when uncertainty exists about potential harm—the strong association between arrested labor and CPD (40-50% of cases) mandates a low threshold for surgical intervention 1
• Do not continue oxytocin if evidence of CPD emerges, as ecbolic agents are best avoided in this setting 1
• Do not wait for formal arrest criteria (historically 2-4 hours) if clinical examination reveals concerning findings like excessive molding or malposition 1
• Graph cervical dilatation during labor to objectively compare pre-arrest and post-arrest progression rates, which improves prognostic accuracy 1