Cephalopelvic Disproportion

Question 1

What are the ideal diameters of the pelvic brim, cavity and outlet?

Answer 1

Brim
AP: 11.5
Transverse: 12.5

Cavity
AP: 12.5
Transverse: 12.5
Ischial spines: 10.5 cm apart

Outlet
Ap: 12.5
Transverse: 11.5

Question 2

What is the ideal subpubic angle and inter tuberous diameter?

Answer 2

Subpubic angle: 85 degrees

Inter tuberous diameter: 10 cm

Question 3

What are the types of pelvic abnormalities with specific examples of each?

Answer 3

• small pelvis:
  Round/ gynaecoid
  Long oval or anthropoid

- abnormal shape/ bone development: 
Triangular brim: android
Flat brim: platypelloid 
Rachitic 
Osteomalacic 

• disease or injury
  Spinal kyphosis
  Pelvic tumours or fractures
  Effect of polio on limbs
• congenital
  Absent sacral alae
  High assimilation

Question 4

What are the two types of CPD and the differences between them?

Answer 4

Absolute: normal size babies but a small or abnormal shaped pelvis
OR contracted pelvis

Relative: normal shaped pelvis but a large baby/ malposition of the fetal head. Occurs in the patois patient

Question 5

What are the dangers of CPD?

Answer 5

Increase in fetal mortality and morbidity due to instrumental delivery

Uterine rupture especially in the parous patient

Bladder damage with the formation of vesico- vaginal fistula due to a sloughing of the bladder base

Question 6

What would make one suspicious of CPD

Answer 6

• patient measuring less than 150 cm
• brim index of less than 85
• high head that cannot be made to engage
• past obstetric history
• pelvimetry- clinical, X-ray or ct- poor predictive value

Hard to predict in primigravid (conduct as a trial of labour)

Question 7

How do you diagnose CPD?

Answer 7

HAS TO BE DIAGNOSED IN LABOUR

-Pelvic assessment 
Can sacral promontory be tipped 
Sacral shape/ contour 
Convergent or divergent  side walls 
Retropubic and subpubic angle 
Inter tuberous diameter 

However This is rarely done in labour

Diagnosis in labour:

• delay in cervical dilatation on the partogram - if alert line in crossed, assess for cause and manage
• no change in level/ station of presenting part (head 3/5 or more)
• other causes of delay in labour excluded
• increased caput and molding of fetal head (3+ moulding)

Question 8

If there was a previous c section for CPD caused by a contracted pelvis should a VBAC be attempted?

Answer 8

No

Question 9

When can a trial of labour be attempted in patients with previous CPD?

Answer 9

If the previous CPD was due to malposition (such as OP or transverse position of the fetal head)

Question 10

What is the size and shape of the female pelvis influenced by?

Answer 10

1) genetic factors
2) nutrition
3) socio economic factors
4) infancy and pubertal factors

Question 11

When can disproportion at the pelvic inlet be excluded?

Answer 11

If 2/5 or less head above the brim

Question 12

How do you grade moulding?

Answer 12

Nil: bones normally separated
+- touching each other
++- overlapping but digitally separated
+++- overlapping but inseparable digitally

Question 13

What are differentials of poor progress of labour? Using the 3 p’s

Answer 13

Patient:
Pain
Bladder full
Dehydrated

Power:
Inadequate contractions
Ineffective contractions

Passenger: 
Lie 
Presentation
Size of fetus 
Twins
Fetal head not engaged 

Passage:
Membranes not yet ruptured
Pelvis inadequate