Obstetrics and Gynaecology · MU Sofia

29. Contracted pelvis - types, diagnosis. Mechanical dystocia - management

Covers the types of contracted pelvis, including a table comparing generally contracted, flat, transversely contracted, asymmetric and rare forms, and the grading by true conjugate. Then walks through diagnosis by history, examination, pelvimetry and tests of disproportion, followed by mechanical dystocia with its signs, warning signs of rupture and complications. Ends with management options for severe, borderline and obstructed labour.

Inside: 5 sections · 1 table · 16 flashcards · 2 min

Topic 29 of 61 in the MU Sofia syllabus for Obstetrics and Gynaecology (Dental Medicine, Year 4). The free AceMed note covers it in 5 sections, about 282 words (2 min of reading), with 16 flashcards.

In this note

  1. Introduction
  2. Types
  3. Diagnosis
  4. Mechanical dystocia and obstructed labour
  5. Management

Introduction

A contracted pelvis is one with a diameter short enough to hinder normal labour. Today it is less common (better nutrition, less rickets), but cephalopelvic disproportion (CPD), a mismatch between the head and the pelvis, still causes obstructed labour.

Types

Grading by the true conjugate: 9–10 cm mild (I), 7.5–9 cm moderate (II), < 7.5 cm severe (III, absolute indication for caesarean section).

Diagnosis

  • History: rickets, pelvic fracture, previous difficult or obstructed labour.
  • Height < 145–150 cm, abnormal gait or spine, abnormal Michaelis rhomboid.
  • External pelvimetry and internal (vaginal) pelvimetry: diagonal conjugate reached easily, prominent spines, narrow subpubic angle.
  • At term in a first pregnancy, a head that will not engage. Tests of disproportion: Vasten's sign (head level with or above the symphysis = disproportion), Muller–Hillis manoeuvre.
  • Imaging (X-ray or MRI pelvimetry) has limited value and is rarely used.

Mechanical dystocia and obstructed labour

When the passenger cannot pass the passage despite good contractions:

  • Signs: slow or arrested dilatation and descent, caput and moulding, oedematous cervix, haematuria.
  • Late signs of impending rupture: tachycardia, fever, Bandl's ring (pathological retraction ring rising toward the umbilicus), a tender lower segment, fetal distress.
  • Consequences: uterine rupture, fetal hypoxia and death, obstetric fistula (vesicovaginal, from pressure necrosis), infection, PPH.

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