Cephalopelvic disproportion

Cephalopelvic disproportion (CPD) occurs when there is a mismatch between the size of the fetal head and the maternal pelvis causing a difficulty in the safe passage of the fetus through the birth canal.

Pathology

Cephalopelvic disproportion may be caused by the fetal head outgrowing the capacity of the maternal birth canal, or by presentation in a position or attitude that will not allow descent through the pelvis. Untreated, the consequence is obstructed labor, which would endanger the life of both mother and fetus.

Classification

Absolute CPD

Absolute CPD leads to a true mechanical obstruction and causes include:

• permanent (maternal factors): 
  • contracted pelvis 
  • pelvic exostoses 
  • spondylolisthesis
  • anterior sacrococcygeal tumors 
• temporary (fetal factors): 
  • hydrocephalus
  • macrosomia

Relative CPD 

• brow presentation 
• face presentation – mentoposterior 
• occipitoposterior positions 
• deflexed head 

The most frequent cause of CPD is contracted pelvis with an average sized infant.

See also

• dystocia
• shoulder dystocia