Cephalopelvic disproportion

This is when the head is too large for the pelvis. It is a common cause of obstructed labour. Possible causes of cephalopelvic disproportion include:

• large baby (absolute disproportion)
  • hereditary factors
  • postmaturity
  • diabetes
  • multiparity : each succeeding baby (up to about the 5th baby) tends to be larger and heavier
    
    
• abnormal positions (relative disproportion)
  • the normal foetus delivers in the occipito-anterior position. If the head is well flexed in this position then the head is presents with the suboccipito-bregmatic diameter (9.5 cm) and easily passes through the pelvis. Other positions e.g. occipito-posterior, brow, present a much larger diameter (11.5 cm and 13.5 cm respectively).
    
    
• small pelvis
  
  
• abnormal shape to pelvis e.g. rickety or trefoil pelvis
  
  
• abnormality of the genital tract
  • cervix : congenital rigidity, postsurgical scarring
  • vagina : congenital septum
  • fibroids may rarely cause obstruction to labour

Predicting caesarean birth for cephalopelvic disproportion in labour

• do not use pelvimetry for decision making about mode of birth
• do not use the following for decision making about mode of birth, as they do not accurately predict cephalopelvic disproportion:
  • maternal shoe size
  • maternal height
  • estimations of fetal size (ultrasound or clinical examination)

Reference:

• NICE (March 2021). Caesarian Sectiion