Contracted Pelvis: An Informative and Comparative Medical Article

1.Rysbaeva Aiganysh Zhoomartovna.

2.Palanisamy Ruban.

3.Mohammad Arshad.

4.Ayan Alam Khan.

(1.   Instructor, Department of Obstetrics, Gynaecology and Surgical Disciplines, International Medical Faculty, Osh State University, Osh, Kyrgyz Republic.)

(2.   Student, International Medical Faculty, Osh State University, Osh, Kyrgyz Republic.)

(3.   Student, International Medical Faculty, Osh State University, Osh, Kyrgyz Republic.)

(4.   Student, International Medical Faculty, Osh State University, Osh, Kyrgyz Republic.)

Abstract

Contracted pelvis is a significant obstetric condition in which one or more pelvic diameters are reduced, resulting in mechanical difficulty for the passage of the fetus during childbirth. Although its incidence has declined in high-resource regions due to improved nutrition and healthcare, it remains clinically relevant in many low- and middle-income countries. This article reviews the anatomical basis of pelvic contraction, etiology, types, diagnostic methods, obstetric impact, and evidence-based management strategies. It emphasizes pelvimetry, functional assessment through trial of labor, and the importance of distinguishing between inlet, mid-pelvis, and outlet contractions. Comparative analysis of various pelvic shapes—such as gynecoid, android, anthropoid, and platypelloid—and pathological types like rachitic and kyphotic pelvis demonstrates their unique influences on labor mechanics and outcomes. Management options including antenatal planning, active intrapartum monitoring, operative delivery, and cesarean section are presented with clinical reasoning. Preventive public health approaches such as childhood nutrition, prevention of rickets, and reduction of early teenage pregnancy are highlighted. The review concludes that early detection, skilled labor monitoring, and timely operative intervention significantly improve maternal and neonatal outcomes in women with contracted pelvis.

Introduction

The human pelvis plays a central role in childbirth. Its bony architecture must be wide enough, with appropriate diameters and angles, to allow the descent of the fetal head through the birth canal. When the pelvic dimensions are smaller than normal, or when its shape is altered in a way that obstructs labor, the condition is referred to as a contracted pelvis. A contracted pelvis is one of the classical causes of cephalopelvic disproportion (CPD), meaning the fetal head cannot pass through the maternal pelvis. Historically, contracted pelvis was a major cause of maternal and perinatal morbidity and mortality. Although improvements in nutrition, childhood vaccination, and obstetric care have reduced its prevalence globally, it remains clinically relevant, especially in low-resource settings. This article explains the etiology, types, clinical signs, diagnostic methods, obstetric complications, and management strategies of contracted pelvis. A comparative discussion between the major pelvic types and contracted pelvis subcategories is also included.

Anatomy and Normal Pelvic Dimensions

 To understand pelvic contraction, one must first know the obstetric pelvis. It is divided into:

i. Pelvic Inlet (Brim)

Important diameters:

Anteroposterior (true conjugate): ~11 cm

Obstetric conjugate: ~10–10.5 cm

Transverse diameter: ~13 cm

Oblique diameter: ~12 cm

ii. Pelvic Mid-Cavity

Interspinous diameter: ~10–10.5 cm (narrowest plane)

Anteroposterior mid-pelvis diameter: ~11 cm

iii. Pelvic Outlet

Anteroposterior outlet diameter: ~11.5 cm

Transverse outlet diameter (intertuberous): ~11 cm

Any significant reduction in these diameters may result in pelvic contraction.

Definition of Contracted Pelvis

A pelvis is called contracted when one or more of its diameters are reduced beyond the physiological limit, making vaginal delivery difficult or impossible.

Clinically:

Pelvic inlet contracted when obstetric conjugate < 10 cm

Midpelvis contracted when interspinous diameter < 10 cm

Outlet contracted when intertuberous diameter < 8–8.5 cm

However, modern obstetrics emphasizes functional assessment rather than measurements alone, meaning a pelvis may be borderline but functionally adequate.

Etiology of Contracted Pelvis

Contracted pelvis results from congenital or acquired factors:

i. Congenital Causes

Genetic small pelvis, Developmental abnormalities, Achondroplasia or skeletal dysplasias

Congenital hip dislocation affecting pelvic shape

ii. Acquired Causes

 Childhood Nutritional Disorders, Rickets (vitamin D deficiency), Osteomalacia

These affect bone mineralization, leading to soft and deformed pelvic bones.

iii. Infectious Diseases

Poliomyelitis, Tuberculosis of spine (Pott's disease) → kyphosis → funnel pelvis

iv. Trauma

Pelvic fractures, Asymmetry from accidents

 Metabolic/Endocrine Disorders, Osteogenesis imperfecta, Endocrine issues affecting bone growth

v. Environmental and Social Factors

Malnutrition

Early teenage pregnancy before pelvic growth is complete

Classification of Contracted Pelvis

 According to the Pelvic Plane Involved

1. Inlet contraction

2. Mid-pelvis contraction

3. Outlet contraction

4. General contraction (all planes reduced)

 According to Pelvic Shape (Caldwell–Moloy Classification)

1. Gynecoid pelvis – normal, most suitable for childbirth

2. Android pelvis – funnel-shaped, narrow anterior segment

3. Anthropoid pelvis – long AP diameter, narrow transverse

4. Platypelloid pelvis – wide transverse, short AP diameter

According to Etiology

Rachitic pelvis

Kyphotic pelvis

Scoliotic pelvis

Robert’s pelvis (transverse arrest)

Pathophysiology: How a Contracted Pelvis Affects Labor

The mechanism of labor depends on moulding, fetal positioning, and uterine forces. When pelvic dimensions are reduced:

i. Engagement Failure

The fetal head does not descend into the pelvis.

ii. Abnormal Presentations

Deflexed head

Occipitoposterior position

Brow or face presentations

iii. Prolonged and Obstructed Labor

Leading to:

Maternal exhaustion

Uterine rupture risk

Fetal hypoxia

Postpartum hemorrhage

CPD (Cephalopelvic Disproportion) a mismatch between fetal head size and pelvic size → major indication for operative delivery.

Clinical Features Suggesting Contracted Pelvis

i. Antenatal Clues

Small maternal stature (<145 cm)

History of obstructed or difficult labor

Looming diagonal conjugate < 11.5 cm

ii. Intrapartum Clues

High fetal head despite good contractions

Persistent 5/5 or 4/5 head above pelvic brim

Molding and caput succedaneum

Failure to progress

Floatation of the head and non-engagement by 38 weeks in primigravida suggest pelvic contraction.

Diagnosis

Diagnosis of contracted pelvis involves clinical assessment, imaging, and labor observation.

i. Clinical Pelvimetry

Performed by trained obstetricians.

Key Components:

Diagonal conjugate measurement (per vaginal)

Ischial spines (if very prominent → mid-pelvis contraction)

Subpubic angle

Intertuberous diameter (perineal test)

Sacral curvature

ii. Imaging Pelvimetry

X-ray pelvimetry (in selected cases)

CT pelvimetry (accurate but rarely needed)

MRI pelvimetry (radiation-free, used in suspected CPD)

iii. Trial of Labor

A controlled “trial of labor” helps assess functional adequacy of the pelvis. Failure of descent is diagnostic.

Types of Contracted Pelvis: Detailed Explanation and Comparison

Below is a comparison of different contracted pelvis types, their anatomical features, and impact on labor.

i. Gynecoid vs Contracted Pelvis (General Contraction)

Feature- Normal Gynecoid -Generally Contracted Pelvis Shape- Round Overall smaller dimensions

Inlet- Wide transverse & AP Reduced AP & transverse diameters

Mid-pelvis -Wide interspinous, Narrow interspinous

Outlet  Adequate - Narrow outlet

Labor Outcome- Usually normal       

ii. Android Pelvis (Funnel Pelvis)

Characteristics:

Heart-shaped inlet

Convergent sidewalls

Prominent ischial spines

Narrow mid-pelvis

Labor Issues:

Deep transverse arrest

Persistent occipitoposterior position

Management

Trial of labor possible in mild cases =High rate of C-section

i. Anthropoid Pelvis

Features:

Long AP diameter, Narrow transverse, posteriorly located sacrum

Labor Outcome: Favors occipitoposterior (OP) position

Vaginal delivery often possible, assisted vaginal delivery may be needed

ii. Platypelloid Pelvis

Features:

Wide transverse inlet, extremely short AP diameter

Labor Complications:

Failure of engagement, transverse arrest

Management:

C-section often required

iii. Rachitic Pelvis

Due to childhood rickets → soft bones, pelvic deformities.

Features:

Flattened sacrum, prominent sacral promontory, reduced AP diameter, “Rickety rosary” history in childhood

Outcome:

Classical inlet contraction, higher CPD risk

iv. Kyphotic Pelvis (High Promontory Pelvis)

Seen in spinal tuberculosis.

Features:

Forward-tilted pelvis, narrow pelvic inlet

Problem:

Obstruction at inlet, fetal deflexion

v. Asymmetrical Pelvis

Caused by fractures or scoliosis.

Features:

Uneven pelvic dimensions, oblique arrest in labor.

Obstetric Complications of Contracted Pelvis

i.  Maternal Complications

1. Prolonged labor

2. Obstructed labor

3. Uterine rupture

4. Postpartum hemorrhage

5. Injury to birth canal

6. Exhaustion, dehydration, ketoacidosis

7. Increased operative complications

ii. Fetal Complications

1. Birth asphyxia

2. Intracranial hemorrhage

3. Caput and molding

4. Neonatal hypoxia

5. Stillbirth or early neonatal death

Management of Contracted Pelvis

Management depends on the severity, type of contraction, fetal size, and previous obstetric history.

 Antenatal Management

 Early Identification, measure maternal height, radiological pelvimetry if needed, evaluate fetal weight.

 Counseling

Explain risks of: CPD  ,Prolonged labor ,Need for C-section

Birth Planning: Elective C-section for significantly contracted pelvis, A trial of labor for borderline or mild cases

Intrapartum Management

 Trial of Labor

Used for borderline cases.

Criteria for trial of labor:

Normal-sized fetus, Adequate contractions, No fetal distress, Skilled obstetrician available

Active Management

Oxytocin augmentation (only if no obvious CPD), Adequate hydration and monitoring, Operative Vaginal Delivery, Forceps or vacuum only if head is engaged

Contraindicated in outlet/mid-pelvis contraction

Cesarean Section

Most reliable and safest in:

True conjugate <10 cm, mid-pelvic contraction, android or platypelloid pelvis with OP position, severe asymmetry, rachitic pelvis.

C-section has reduced maternal mortality associated with contracted pelvis worldwide.

Conclusion

Contracted pelvis remains an important obstetric challenge, particularly in areas with limited healthcare access. Understanding its etiology, types, and diagnostic approach enables timely identification of women at risk of obstructed labor. Clinical pelvimetry, careful monitoring during labor, and the judicious use of cesarean delivery are essential for safe outcomes. Management decisions must be individualized, keeping in mind the balance between pelvic dimensions, fetal size, and labor progress. Through improved childhood health, adequate maternal care, and strengthened health systems, the incidence and complications of contracted pelvis can be significantly reduced.

REFERENCES

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