CONTRACTED PELVIS AND CEPHALOPELVIC DISPROPORTION

DEFINITION: Anatomical definition: It is a pelvis in which one or more of its

main diameters are reduced below average normal by one or more centimetres.

Obstetric definition: It is a pelvis in which one or more of its main diameters are reduced to the extent that interferes with the normal mechanism of labour.

Factors which affect the shape and the size of the pelvis: Several factors contribute to affect the shape and size of the human pelvis, including;

developmental factors, sexual factors (male or female) ,

racial factors (dark and white, Caucasians and Africans, etc.) , nutritional factors (lack of calcium and proteins) ,

and metabolic diseases (as rickets and osteomalacia).

AETIOLOGY:Causes in the pelvic bone:

Developmental causes (Abnormal shape) :Small gynaecoid (generally contracted pelvis), small android, small anthropoid, and small flat platypelloid pelvis (simple non-rachitic pelvis).

Diseases of the pelvic bones and joints :Metabolic diseases :

Rickets; resulting into flat rachitic pelvis and generally contracted pelvis.Osteomalacia: resulting into (triradiate pelvis).

Fractures of the pelvic bones .

Tumours of the pelvic bones. Diseases of the pelvic joints e.g.: T.B.

Causes in the spine: Dorso-lumbar scoliosis,

Lumbar Kyphosis , and Spondylolisthesis.

Causes in the lower limbs: Dislocation of one or both femurs. Atrophy of one or both lower limbs.

Unilateral fracture or tumour . Unilateral lower limb disease (poliomyelitis).

DIAGNOSIS:

History: Bad obstetric history suggestive of contracted pelvis

e.g:. Prolonged labour ending in C.S, fetal birth injury, or still birth (S.B.).

Difficult forceps ending in S.B. or fetal birth injury .

History of trauma or disease of pelvis, spine or lower limbs.

Examination:GENERAL EXAMINATION :

*Height: Short stature < 150 cm, is commonly associated with a contracted pelvis.

* Gait: abnormal gait suggestive of diseases of the lower limb or spines.

* Stigmata of old rickets: as square head, pigeon chest, costal rosary, Harrison’s sulcus, spine deformities and bow legs.

* Dystrophia dystocia syndrome: Short, obese, muscular appearance, male distribution of hair; may have an android pelvis (favouring occipito-posterior position).

* Spines: for deformities in the spines (scoliosis or Kyphosis).

* Lower limb: for abnormalities .

ABDOMINAL EXAMINATION: for evidence suggesting contracted pelvis

Malpresentations; as face, brow, breech and transverse lie .

Non engagement of the fetal head in the last 3 or 4 weeks in a primigravida .

CLINICAL PELVIMETRY :External Pelvimetry :

External pelvimetry at the inlet: it has a little significance as it actually measures the diameters of the false pelvis.

External Pelvimetry at the outlet:

Sub-pubic angle: direct palpation of the ischio-pubic rami (normally obtuse in females).

Bituberous diameter: Roughly admits the 4 knuckles of the closed fist or measured by the pelvimeter (11 cm).

Anterior and posterior sagittal diameters: Measured by Thom's pelvimeter.

NB: Thom’s dictum: The sum of the bituberous and posterior sagittal diameters must exceed 15 cm to allow an average sized head to pass through the pelvic outlet provided that the bituberous diameter is more than 8 cm.

Internal Pelvimetry:It is done through a P.V. examination, at 38 weeks during ANC, or during early labour. The following diameters should be assessed:

1 (Diagonal conjugate :Between the lower border of the symphysis pubis and the promontory of the sacrum.

Normally the diagonal conjugate is 12.5 cm (1.5 cm > true conjugate), and by subtracting 1.5 cm from the diagonal conjugate the length of the true conjugate can be evaluated.Normally the sacral promontory is not easily felt or reached.To measure the diagonal conjugate the head must be not engaged.

2 (Palpation of the sacrum: normally it is concave with smooth concavity from above downwards and from side to side (there is no sudden bent).

3 (Palpation of the sidewalls of the pelvis: normally it is not converging.4 (Estimation of the width of the Sacro sciatic notch: normally it accommodates

2 fingers.5 (Palpation of the ischial spines: normally it is not felt when opening the index

and middle fingers at the same time (not jutting)6 (Palpation of the sub pubic angle: normally it accommodates 2 fingers.

RADIOLOGICAL PELVIMETRY :Lateral view X ray and C.T. scan pelvimetry can assess pelvic diameters, but nowadays is rarely needed. (e.g.; if vaginal breech delivery is attempted).

ULTRASOUND ASSESSMENT OF THE DIAMETERS OF FETAL HEAD

It is the most commonly used method . It can assess the size of the fetal head by use of the following

diameters:Biparietal diameter, ( BPD)Occipto-frontal diameter (OFD)Head circumference (HC).

CEPHALOPELVIC DISPROPORTION (CPD) TESTS:It depends upon the fact that “The head is the best pelvimeter for the pelvis”

Timing: These tests are especially important in a primigravida with unengaged head after 36 weeks.

Pinard’s method :The patient is put in the semi-sitting position with the bladder empty, to bring the foetus in the axis of the pelvic inlet.

The operator right hand is placed over the symphysis pubis and the left hand grasps the fetal head and try to push it downwards and backwards in the pelvis.

The fingers of the right hand placed over the symphysis pubis can determine the degree of disproportion.

Muller-Kerr method :The patient is put in the dorsal position, with the bladder empty.

The index and the middle fingers of the right hand are put in the vagina to perform the steps of the internal pelvimetry and to detect the station of the head in the pelvis.

The thumb of the right hand is put over the symphysis pubis to determine the presence of any disproportion and its degree.

The head is grasped by the left hand and is pushed downwards into the pelvis.

INTERPRETATION OF RESULTS OF CPD TESTS : No disproportion: if the head can be pushed into the pelvis.

Moderate disproportion (1st degree disproportion):The head does not enter the pelvis and is nearly at the same level of the anterior surface

of the symphysis pubis .Vaginal delivery may or may not occur depending upon the undetermined factors of labour (moulding of the head and yielding of the pelvis).

Marked disproportion (2nd degree disproportion):The head overrides the anterior surface of the symphysis.Usually found in cases with marked degree of contracted pelvis.Vaginal delivery cannot occur.

MATERNAL RISKS DURING LABOUR IN CONTRACTED PELVIS

* Prolonged labour and slow dilatation of the cervix (abnormal progress of labour).

*Premature rupture of membranes and prolapse of cord. * Obstructed labour (may end in rupture of the uterus) .

* Higher incidence of instrumental and operative delivery . * Postpartum haemorrhage (due to atony and lacerations).

* Maternal infection (prolonged labour and instrumental delivery). * Necrotic genitourinary fistula.

* Rarely, injury of the joints or nerves from difficult instrumental delivery .

FETAL RISKS DURING LABOUR IN CONTRACTED PELVIS:

* Fetal birth injuries: Intra-cranial haemorrhage,

fractures of the skull , nerve injuries, etc..

* Intrapartum and neonatal asphyxia.

* Prolapse of the cord, due to the high non engaged presenting part.

* Intra-amniotic infection, due to the prolonged early spontaneous ROM.

MANAGEMENT OF LABOUR IN CONTRACTED PELVIS Decision-making: Before allowing labour to continue, early exclusion of indications for C.S. is mandatory: e.g.; Malpresentations, Placenta previa,

Uterine scar of s previous CS or myomectomy, Elderly primigravida etc…

Management according to the degree of CPD:* Moderate degree of cephalo-pelvic disproportion

Trial of labour (TOL) in selected cases (see case selection). C.S. trial of labour is failed or contraindicated.

* Marked degree of cephalo-pelvic disproportion CS if the foetus is living.

Craniotomy for dead foetus.

Trial of labour (TOL)

It is a test of the undeterminable factors of labour in moderate degree of CPD. It is affected by:

Moulding of the head and Yielding of the pelvis.

Efficiency of uterine contractions and Dilatation of the cervix.

Selection of cases for trial of labour :Young healthy primigravida, with a cephalic presentation and moderate degree disproportion.

Cases with bad obstetric history, marked outlet contraction, and post-maturity are better excluded.

Conduct of trial of labour :It must be in a hospital with available facilities for CS.

Proper management of the 1st stage of labourProper assessment of the progress of labour by the use of partogram.Proper and adequate analgesia to avoid maternal exhaustion.

A successful TOL ends by engagement of the head and vaginal deliveryA failed TOL ends by reverting to a C.S.

Termination of TOL by CS is indicated in cases of :

Occurrence of fetal or maternal distress.

Failed progress of labour as evidenced by a well monitored partogram .

Indications of Caesarean section in contracted pelvis: * Marked disproportion if the foetus is living.

* Moderate disproportion if trial of labour is contraindicated or fails.* Markedly contracted outlet.

* Contracted pelvis in elderly primigravida.* Contracted pelvis associated with complications as malpresentations,

or placenta praevia.

Contracted outlet: “Funnel pelvis :”

* Definition: it is a variant of contracted pelvis in which the bituberous diameter is 8 cm or less.

* Features: The pelvic capacity is reduced from above downward. The pelvis is narrow and deep, Sidewalls are converging, Transverse diameter of the outlet is reduced, A.P. diameter of the outlet is reduced.

* Mechanism of labour: Extreme flexion and moulding occurs at the outlet with backwards displacement of the fetal head. N.B.; Contraction of the outlet interferes with long anterior rotation in O.P. positions.

* Management: According to “Thom’s dictum”, when the sum of the bituberous and the

posterior sagittal diameters is > 15 cm, the bituberous is > 8 cm and the sub-pubic angle is not very narrow: a generous episiotomy is performed and low

forceps may be applied .If the sum of the bituberous and the posterior sagittal is <15 cm C.S. is performed.