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)