Cephalopelvic disproportion (CPD) occurs when there is a mismatch between the size of the fetal head and the maternal pelvis causing 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.
Absolute CPD
Absolute CPD leads to a true mechanical obstruction and causes include:
-
permanent (maternal factors):
contracted pelvis
pelvic exostoses
anterior sacrococcygeal tumors
-
temporary (fetal factors):
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.