2d:I[856015,["/_next/static/immutable/chunks/1xzisbplk9czp.js","/_next/static/immutable/chunks/3j2i1faptc_-9.js","/_next/static/immutable/chunks/0fma7nlq6immz.js","/_next/static/immutable/chunks/08tq8rmv423j5.js","/_next/static/immutable/chunks/1chr5wkk3j58k.js","/_next/static/immutable/chunks/37kmmh_zm4dov.js","/_next/static/immutable/chunks/311zvdjfxff-f.js","/_next/static/immutable/chunks/1a_hqhrsle_n_.js"],"default"] 2e:T50ea,

Summary Table

Category	Details
Risk Factors	Short maternal stature, android/platypelloid pelvis, macrosomia (fetal weight >4000 g), gestational diabetes, postterm pregnancy, prior CPD
Etiology	Mismatch between the fetal head dimensions and the maternal pelvic capacity, either from a large fetus, a contracted pelvis, or malpresentation
Patient Presentation	Active labor with failure to progress despite adequate uterine contractions (Montevideo units >200 for 2+ hours)
Classic Physical Exam	Cervical dilation arrest or arrest of fetal descent, persistent high station, caput succedaneum, excessive molding, positive Muller-Hillis maneuver
Key Diagnostic Results	Partograph showing arrest disorder, clinical pelvimetry suggesting contracted pelvis, labor curve analysis (Friedman curve deviation)
Management	Cesarean delivery when true CPD is confirmed; oxytocin augmentation only if contractions are inadequate (to rule out inadequate uterine force first)
Keywords	"Failure to progress," "arrest of dilation," "arrest of descent," "adequate contractions," "no cervical change," "high station"

1. Pathophysiology

The fundamental concept behind cephalopelvic disproportion is a mechanical obstruction to vaginal delivery. For a fetus to pass through the birth canal, three variables must align: the power (uterine contractions), the passenger (fetal size, lie, presentation, and attitude), and the passage (bony pelvis and soft tissues). CPD occurs when the passenger is too large relative to the passage, regardless of how strong the power is.

The maternal bony pelvis has three critical planes. The pelvic inlet (obstetric conjugate, normally >10 cm) is where engagement occurs. The midpelvis (interspinous diameter, normally >10 cm) is the narrowest fixed bony dimension and the most common site of arrest. The pelvic outlet (intertuberous diameter, normally >8 cm) rarely causes obstruction alone. Contracture at any of these levels can prevent descent.

On the fetal side, the key measurement is the biparietal diameter (BPD), which averages 9.5 cm at term. Macrosomic fetuses, hydrocephalic fetuses, or fetuses in deflexed attitudes (brow or face presentation) present larger diameters to the pelvis, creating disproportion even in a normal-sized pelvis. A persistent occiput posterior position, for example, presents the occipitofrontal diameter (11.5 cm) instead of the smaller suboccipitobregmatic diameter (9.5 cm), effectively creating a functional CPD.

The clinical consequence of this mismatch is arrest of labor. Despite adequate contractions, the cervix stops dilating (arrest of dilation) or the fetal head fails to descend through the pelvis (arrest of descent). Prolonged obstruction can lead to uterine rupture, fetal hypoxia, and obstetric fistula formation if not recognized and managed.

2. Classification and Clinical Manifestation

Pelvic Types (Caldwell-Moloy Classification)

Pelvic Type	Shape	Inlet Characteristics	Clinical Significance
Gynecoid	Round/oval	Transverse and AP diameters roughly equal	Most favorable for vaginal delivery; present in ~50% of women
Android	Heart-shaped/triangular	Narrow anterior segment, prominent ischial spines	Associated with deep transverse arrest and persistent OP; higher CPD risk
Anthropoid	Long AP oval	AP diameter exceeds transverse	Favors OP or OA delivery; moderate CPD risk
Platypelloid	Flat/wide oval	Wide transverse, short AP diameter	Inlet obstruction; highest CPD risk; least common

Arrest Disorders in Labor

Disorder	Definition	Nullipara	Multipara
Arrest of dilation	No cervical change despite adequate contractions	No change for 4 hours with adequate contractions (or 6 hours with inadequate contractions)	No change for 4 hours with adequate contractions
Arrest of descent	No descent of presenting part in the second stage	No descent for 3 hours (with epidural) or 2 hours (without)	No descent for 2 hours (with epidural) or 1 hour (without)
Failed induction	Inability to generate regular contractions and cervical change	Failure to achieve active labor after oxytocin for 12-18 hours with ruptured membranes	Same criteria

Fetal Malpresentations Contributing to Functional CPD

Presentation	Presenting Diameter	Diameter Size	Prognosis
Vertex, well-flexed (OA)	Suboccipitobregmatic	9.5 cm	Favorable
Vertex, deflexed (military)	Occipitofrontal	11.5 cm	Unfavorable
Brow	Mentovertical	13.5 cm	Cannot deliver vaginally (largest diameter)
Face (mentum anterior)	Submentobregmatic	9.5 cm	Vaginal delivery possible
Face (mentum posterior)	Submentobregmatic	9.5 cm	Cannot deliver vaginally (neck cannot extend further)

3. Diagnostic Workup

Test	Role	Key Findings
Partograph	Best initial monitoring tool	Crossing the action line, flat dilation/descent curves
Clinical pelvimetry	Bedside assessment of pelvic dimensions	Diagonal conjugate <11.5 cm (suggests inlet contracture), prominent ischial spines, narrow subpubic arch (<90 degrees)
Intrauterine pressure catheter (IUPC)	Quantify contraction adequacy	Montevideo units (MVU); adequate = >200 MVU over 10 minutes
Ultrasound	Estimated fetal weight, fetal position	EFW >4000 g (or >4500 g in diabetic mothers), persistent OP position
CT/MRI pelvimetry	Rarely used; confirmatory for pelvic dimensions	AP and transverse diameters below normal thresholds

CPD is fundamentally a clinical diagnosis made retrospectively during labor. There is no single test that definitively predicts CPD before a trial of labor. This is a heavily tested concept: the exam will present a patient in active labor who is not progressing and ask you to determine why.

The first step when labor arrests is not to diagnose CPD immediately. Instead, you must first determine whether the contractions are adequate. An IUPC is placed to measure Montevideo units. If contractions are inadequate (<200 MVU), the problem is the power, not the passage, and you augment with oxytocin. Only after you have confirmed adequate contractions (>200 MVU for at least 2-4 hours) with no cervical change can you label the arrest as CPD.

Clinical pelvimetry during prenatal visits can raise suspicion. If the diagonal conjugate (measured from the lower border of the symphysis to the sacral promontory) is <11.5 cm, the obstetric conjugate (which is about 1.5 cm shorter) may be <10 cm, suggesting inlet contracture. However, clinical pelvimetry alone is not sufficient to recommend a primary cesarean. A trial of labor is still indicated unless there is an absolute contraindication.

Ultrasound for estimated fetal weight is important but carries a margin of error of 15-20%. An EFW of 5000 g in a non-diabetic mother or 4500 g in a diabetic mother is considered a threshold where elective cesarean may be offered without a trial of labor. Below these thresholds, suspected macrosomia alone is not an indication for cesarean.

4. Management and Treatment

Clinical Scenario	Next Best Step	Details
Arrest of dilation + inadequate contractions	Oxytocin augmentation	Low-dose protocol: start 0.5-2 mU/min, increase by 1-2 mU every 30-40 min; goal >200 MVU
Arrest of dilation + adequate contractions for 4+ hours	Cesarean delivery	True CPD confirmed; further oxytocin will not overcome a mechanical obstruction
Arrest of descent + adequate contractions for 2-3+ hours	Cesarean delivery	Operative vaginal delivery (forceps/vacuum) only if station is +2 or lower
Suspected macrosomia >5000 g (non-diabetic) or >4500 g (diabetic)	Elective cesarean	Without trial of labor
Prior CPD with similar or larger estimated fetal size	Discuss repeat cesarean	A trial of labor (TOLAC) may still be offered depending on clinical context

When a patient in active labor shows no progress, the first intervention is to assess contraction adequacy. Place an IUPC if external monitoring is ambiguous. If MVU is <200, begin oxytocin augmentation. Standard low-dose protocol begins at 0.5-2 mU/min and increases by 1-2 mU/min every 30-40 minutes, titrating to achieve 3-5 contractions per 10 minutes with MVU >200. Amniotomy (artificial rupture of membranes) can also be performed simultaneously to augment labor.

If contractions are adequate (MVU >200) and the cervix has not changed for 4 hours, or if contractions remain inadequate after maximum oxytocin and 6 hours have passed without cervical change, the diagnosis is arrest of active phase, and the next step is cesarean delivery. Continuing oxytocin beyond this point increases the risk of uterine rupture, chorioamnionitis, and fetal distress without meaningful benefit.

In the second stage, if descent has arrested for the defined time threshold (2-3 hours depending on parity and epidural status), you must decide between operative vaginal delivery and cesarean. Operative vaginal delivery (vacuum or forceps) is only appropriate if the fetal head is at station +2 or below, there is no suspected CPD at the midpelvis level, and the operator is experienced. If the station remains high (0 or +1), this strongly suggests true CPD, and cesarean is indicated. Attempting forceps at a high station ("high forceps") is contraindicated due to the risk of catastrophic maternal and fetal injury.

Contraindications to note: Oxytocin is contraindicated in the setting of prior classical (vertical) uterine incision, as the risk of uterine rupture is too high. In a patient with a prior low transverse cesarean, oxytocin may be used cautiously during TOLAC but requires continuous fetal monitoring.

5. Differential Diagnosis and Distractors

Differential Diagnosis	Why It Looks Similar	Key Discriminator
Inadequate uterine contractions (hypotonic dysfunction)	Also presents as failure to progress with arrested dilation	MVU <200 on IUPC; responds to oxytocin augmentation. True CPD does not respond to oxytocin.
Hypertonic uterine dysfunction	Labor is not progressing	Painful, frequent, uncoordinated contractions with no effective dilation, typically in latent phase. Treated with rest and sedation, not cesarean.
Persistent occiput posterior (OP)	Arrest of descent, prolonged second stage	Fetal head is palpated with occiput directed posteriorly. May resolve with manual rotation or maternal repositioning. True CPD at the bony level will not resolve with position changes.
Cervical dystocia	Arrested dilation despite adequate contractions	Rare; the cervix itself is the problem (scarring from prior procedures such as cone biopsy). Fetal head may be well-engaged and at good station, unlike CPD.
Shoulder dystocia	Mechanical obstruction during delivery	Occurs after the head has already delivered ("turtle sign"). This is an emergency at the outlet, not an arrest of dilation or descent during labor.
Chorioamnionitis	Can be associated with prolonged labor	Maternal fever, tachycardia, uterine tenderness, foul-smelling amniotic fluid. This is a consequence of prolonged labor, not the cause of arrest.

6. Traps and High-Yield Pearls

The single most common trap on this topic is diagnosing CPD prematurely before confirming contraction adequacy. The vignette will describe a patient with arrested dilation and ask for the next step. Students who jump straight to cesarean delivery will get the question wrong. The correct answer is almost always to assess or augment contractions first. You cannot call it CPD until the power has been proven adequate and labor still fails to progress.

A second common trap involves estimated fetal weight. A vignette may mention an EFW of 4200 g and tempt you to recommend cesarean for macrosomia. However, in a non-diabetic mother, the threshold for elective cesarean based on weight alone is 5000 g, not 4000 g or 4500 g. Below that threshold, a trial of labor is appropriate regardless of the estimated weight.

Third, remember that clinical pelvimetry and prenatal ultrasound cannot reliably predict CPD. The exam may offer a distractor like "schedule elective cesarean due to small pelvis on clinical exam." This is incorrect. The only reliable way to diagnose CPD is through a trial of labor with documented adequate contractions and failure to progress.

The core competency being tested is your ability to sequentially troubleshoot labor arrest: first rule out inadequate power, then confirm a true mechanical obstruction, and only then proceed to cesarean delivery. The test-writer wants to see that you understand the algorithm, not just the diagnosis.

1e:["$","$L2d",null,{"article":{"id":"62310a12-6478-4bfc-9a78-1c351bd70cd0","title":"Cephalopelvic Disproportion","content":"$2e","category":"Reproduksi","created_at":"2026-05-15T15:15:34.417321+00:00","status":"published","subcategory":null},"questionCount":0,"sections":[{"id":"section-pathophysiology","num":"01","title":"Pathophysiology"},{"id":"section-classification-and-clinical-manifestation","num":"02","title":"Classification and Clinical Manifestation"},{"id":"section-diagnostic-workup","num":"03","title":"Diagnostic Workup"},{"id":"section-management-and-treatment","num":"04","title":"Management and Treatment"},{"id":"section-differential-diagnosis-and-distractors","num":"05","title":"Differential Diagnosis and Distractors"},{"id":"section-traps-and-high-yield-pearls","num":"06","title":"Traps and High-Yield Pearls"}],"hasSummaryTable":true}]