cephalopelvic disproportion

Last edited 04/2021 and last reviewed 04/2021

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