DEFINITION

• Anatomical - It is a pelvis in which one or more of its diameters is reduced below the normal by one or more centimeters.

• Obstetric - It is a pelvis in which one or more of its diameters is reduced so that it interferes with the normal mechanism of labour.

FACTORS INFLUENCING THE SIZE AND SHAPE OF THE PELVIS

• Developmental factor: hereditary or congenital.

• Racial factor.

• Nutritional factor: malnutrition results in small pelvis.

• Sexual factor: as excessive androgen may produce android pelvis.

• Metabolic factor: as rickets and osteomalacia.

• Trauma, diseases or tumours of the bony pelvis, legs or spines.

• AETIOLOGY

• Developmental (congenital):

• Small gynaecoid pelvis (generally contracted pelvis).

• Small android pelvis.

• Small anthropoid pelvis [apelike pelvis with a long anteroposterior diameter and a narrow transverse diameter]

• Simple flat pelvis

• Naegele’s pelvis: absence of one sacral ala.

• Robert’s pelvis: absence of both sacral alae.

• High assimilation pelvis: The sacrum is composed of 6 vertebrae.

• Low assimilation pelvis: The sacrum is composed of 4 vertebrae.

• Split pelvis: splitted symphysis pubis.

• Metabolic:

• Rickets.

• Osteomalacia

• Traumatic: as fractures, dislocation of joints, improper osteosynthesis in fracture

• Neoplastic: tumors of bony pelvis

• Unfavourable living conditions

• CLASSIFICATION

• Classified by:-

• A) type of distortion of pelvic architecture

• B) degree of contraction

• A) CLASSIFICATION BY PELVIC ARCHITECTURE

1. Pelvis aequabiliter justo minor

• - characterised by general reduction of all diameters; equally shortened usually by 1-2cm

• Occurs in short and subtile women and in women with signs of infantilism

• women with massive skeletal bones and developed muscles, the pelvis has masculine features such as narrow sacrum, narrow pubic outlet {funnel-shaped)

2. Flat Pelvis

• reduced anteroposterior diameters with normal transverse and oblique diameters

• Has 2 types of contracture

a) Simple flat (or platypellic) pelvis

• Entire sacral platform is dislocated toward the symphysis hence all the anteroposterior diameters of all pelvic planes are reduced

b) Flat rachitic

• anteroposterior diameter of the pelvic inlet only is reduced

3. Generally Contracted Pelvis

• All diameters reduced, but the anteroposterior diameters are shortened greater then the others

• Usually connected with infantilism and rickets of the childhood

Rare forms of contracted pelvis

• Coxalgic pelvis

• Otto’s pelvis – develop as result of inflammatory process in the hip or knee

• Naegele (Obliquely contracted) pelvis – underdevelopment of sacral wings.

• Robert (transversely contracted) pelvis

• Beaked (rostrate) pelvis – underdevelopment of both sacral wings

• Spondylolithetic pelvis – formed due to partial dislocation of last lumbar vertebra in front of 1st sacral vertebra

• Osteomalacic pelvis

B) Classification By Degree Of Contracture

i. First degree: true conjugate <11cm but not <9cm, spontaneous delivery is possible

ii. Second degree: true conjugate = 9-7.5cm spontaneous delivery possible but complications may arise

iii. Third degree: true conjugate 7.5-6cm spontaneous delivery impossible, use C-section

iv. Fourth degree: true conjugate <6cm, impossible delivery, only way is C-section ; also known as absolutely contracted pelvis

Diagnosis

A. History

• Rickets: is expected if there is a history of delayed walking and dentition.

• Trauma or diseases: of the pelvis, spines or lower limbs.

• Infantilism

• Previous tuberculosis of bones and joints

• Bad obstetric history: e.g. prolonged labour ended by;

▫ difficult forceps,

▫ caesarean section or

▫ still birth.

• . Shape of Michaelis rhomboid (corresponding diamond-shaped area in females )

• Normal : regular shape

• Justo minor: diamond shaped

• Flat rachitic pelvis: upper portion is smaller

• Generally contracted pelvis : rhomboid elongated in vertical direction

Pelvimetry

• It is assessment of the pelvic diameters and capacity done at 38-39 weeks. It includes:

• Clinical pelvimetry:

▫ Internal pelvimetry for:

inlet,

cavity, and

outlet.

▫ External pelvimetry for:

inlet and 

outlet.

• Imaging pelvimetry:

▫ X-ray.

▫ Computerised tomography (CT).

Magnetic resonance image

Pregnancy

• 1st half uneventful

• 2nd half may develop toxaemia, head fails to enter pelvic inlet, may develop dyspnoea, tachycardia & fatigue

• Failure of head to engage increase mobility of fetus hence increase risk of breech presentation, face & brow presentation

• Mobile head doesn’t divide amniotic fluid into 2 portions, so the fluid is often discharged prematurely

Mechanism of Labour

1. In justo minor:-

1st feature – strongly flexed vertex

2nd feature – sagittal suture of the engaging head aligns with an oblique diameter of the pelvic inlet plane

- the strongly flexed vertex is performs the same movements as in normal mechanism of labour: internal rotation, extension, external rotation except that the movements are slower and requires more effort from the parturient

- because of the narrow pubic angle, the posterior cranial fossa cannot come in direct contact with the symphysis as the head passes the pelvic outlet planem therefore it gets displaced toward the perineum, the perineal tissues undergo great extension and deep laceration may occur

- the head of the delivered fetus is elongated in the direction of the occiput and swelling is formed in the region of the posterior fontanelle

2. In flat rachitic pelvis

1st feature – sagittal suture aligns with the transverse diameter of the pelvic inlet plane for a long time

2nd feature – insignificant deflexion of the vertex as a result of which the anterior fontanelle assumes the position below the posterior fontanelle

3rd feature – asynclitism (the presentation during labor of the head of the fetus at an abnormal angle )

3. In simple flat pelvis

The process passes as flat rachitic pelvis till the mid cavity where internal rotation and further descent cannot occur due to persistence of flattening of the pelvis and contracted outlet. So deep transverse arrest is common and vaginal delivery is obstructed.

4. Generally contracted pelvis

similar as justo minor or flat pelvis

Conduct of Labour

• Should be under observation of physician

• Casesarean section is performed on women with the 3rd & 4th stage degree of contracture at the end of pregnancy or at the beginning of dilation stage

• Watchful expectancy is recommended for 1st & 2nd stage, surgery only indicated if complications develop

• Women examined carefully & history taken on admission, internal organs inspected & measure pelvis, vaginal examination

• Prevention of early discharge of amniotic fluid by placing the woman in bed while lying on the side where occiput is identified, after discharge, another vaginal examination is conducted

• Labour is prolonged & tiring, should give nutritive & easily assimilable food

• Catheterization of urinary bladder if urination is difficult

• Uterine stimulants given to patients with uterine inertia (Failure of the uterus to contract with normal strength and duration and at normal intervals during labour)

• If patient fatigued, give rest, promedol or pantopon given s/c, ether given to inhale for 20-30min

• Ether also calms down violent contractions and prevent uterine rupture

• Observe fetal heart function & steps to prevent fetal asphyxia should be taken

Indications of caesarean section

• Cephalopelvic disproportion

• Threatened rupture of uterus

• Formation of fistula in uterus

• Unfavourable engagement of the head

• Other complications that worsens prognosis eg; elderly primigravida

Complications

• Maternal:

▫ During pregnancy:

Incarcerated retroverted gravid uterus.  

Malpresentations.

Pendulous abdomen.                        

Nonengagement.

Pyelonephritis especially in high assimilation pelvis due to more compression of the ureter.

▫ During labour:

Inertia, slow cervical dilatation and prolonged labour.

Premature rupture of membranes and cord prolapse.

Obstructed labour and rupture uterus.

Necrotic genito-urinary fistula.

Injury to pelvic joints or nerves from difficult forceps delivery.

Postpartum haemorrhage.

• Foetal:

▫ Intracranial haemorrhage.     

▫ Asphyxia.               

▫ Fracture skull.

▫ Nerve injuries.                   

▫ Intra-amniotic infection.

CPD

Disproportion in size between the fetal head and the maternal pelvic cavity, which causes difficulty in the labour and endanger the fetal life .

Cause of CPD:

I. Maternal :-

Contracted pelvis:-

a. Developmental:- android, anthropoid and platypelloid pelvis.

b. Congenital defect

c. Acquired defect:- rachitic pelvis, osteomalacic pelvis, any disease or injury of bone.

II. Foetal:- Malpresentation, malposition, hydrocephaly, Macrosomic baby.

DIAGNOSIS OF CONTRACTED PELVIS

Diagnosis of CPD is very difficult. This is because it is difficult to estimate exactly how much the mother's ligaments and joints will 'give' or relax before labor starts.

Contraction may be at the level of brim, cavity, outlet or combined.

HISTORY:

GENERAL: Rickets, Osteomalacia, Poliomyelitis, TB

OBSTETRIC: Previous Deliveries

PHYSICAL EXAMINATION:

HEIGHT: high risk <140 cm

SPINAL / CHEST WALL DEFORMITIES

WADDLING GATE

OBSTETRIC EXAMINATION:

Unengaged head in the Primi at term

Deflexed attitude at the onset of labour

EXTERNAL PELVIMETRY:

Poor accuracy, no role in modern Obstetrics

1. Transverse Diameter of Outlet: between two inner surface of Ischial tuberocities

= 10.5 – 11 cm

2. Antero-Posterior Diameter of Outlet: between tip of sacrum to symphysis pubis

= 12.5 cm

3. Posterior Saggital Diameter of Outlet:

between the mid point of TD to the sacral tip

= 7 cm

INTERNAL PELVIMETRY:

INSTRUMENTS vs VAGINAL EXAMINATION

VAGINAL ASSESSMENT OF PELVIC CAVITY

CLINICAL PELVIMETRY

DORSAL LITHOTOMY POSITION

ASK TO EMPTY BLADDER

USE INDEX & MIDDLE FINGERS

1. SACRAL PROMONTARY

DIAGONAL CONJUGATE (12.5 cm)

TRUE CONJUGATE = DC – 1.5 -2 cm

diagonal conjugate

a radiographic measurement of the distance from the inferior border of the symphysis pubis to the sacral promontory. The measurement, may also be determined by vaginal examination.

CLINICAL PELVIMETRY:

2. SACRAL CURVATURE

3. PELVIC SIDE WALLS

4. SACRO-SCIATIC NOTCH (Length of the sacro-tuberous Ligaments)

5. ISCHIAL SPINES: BISPINOUS DIAMETER

6. SUB-PUBIC ARCH:

7. FIST IN BETWEEN THE ISCHIAL TUBEROSITIES

DIAGNOSIS OF CONTRACTED PELVIS

RADIOLOGICAL ESTIMATION:

1. X-RAY PELVIMETRY:

Pelvis- Lateral view, superio-inferior view, Outlet, Antero-posterior View

2. USG

MANAGEMENT OF LABOUR IN CONTRACTED PELVIS

HIGH RISK PREGNANCY-----REFERRED TO SPECIALISED CENTRE

MODE:

1. ELECTIVE LSCS

2. TRIAL LABOUR

ELECTIVE LSCS

INDICATIONS:

1. Gross CPD

2. Elderly Primi gravida

3. Toxemia of pregnancy

4. BOH

5. Post maturity

6. Malpresentation

TIMING:

1. Elective setting – planned procedure

2. Emergency setting – onset of Labour

lower uterine segment well formed

less bleeding – due to contraction

adequate intra-uterine time for maturation

TRIAL LABOUR

INDICATIONS:

1. Mild / suspicion of CPD

GOOD PROGNOSIS

Good Uterine contraction

Early engagement of Head

Rupture after full dilatation

Good effacement &dilatation

Flat pelvis

Vertex presentation with anterior position

BAD PROGNOSIS

Weak Uterine contraction

Slow descent of the head

Premature rupture of membrane

Uneffaced cervix

Occipito-posterior position

Android pelvis

Other than vertex presentation

MANAGEMENT OF LABOUR IN CONTRACTED PELVIS

THE ROLE OF FORCEPS

NO ROLE; DO NOT USE IF HEAD IS NOT ENGAGED

SYMPHYSIOTOMY - PUBIOTOMY

PRIOR TO THE ERA OF ANTIBIOTICS

DESTUCTIVE OPERATION:

CRANIOTOMY