Understanding Labor Progress: Failure to Descend, Progression, and CPD

Question
Dear Dr. Rappaport,
Is there a difference between failure to descend, failure to progress and cpd as reasons for a c/s?  
If there is, could you briefly describe.
Thanks so much, Ruth

Answer
When you are in active labor, your cervix should dilate approximately 1cm per hour until it reaches full dilatation (10cm). If you do not prfogress to full dilatation, this is called "failure to progress". Usually, we first try to stimulate the labor by giving pitocin to give you more effective contractions. HOwever, if there still is no further dilatation, a cesarean sectiion is performed due to "failure to progress in labor".  If you do reach full dilatation, and start to push. The baby usually will come down and go through the birth canal to effect a vaginal delivery. If the baby's head (cephalus) is larger than your pelvic bones and it cannot negotiate the passage through the bones, a cesarean section is done for cephalopelvic disproportion (CPD), because the baby's head could not get through.  If you reach full dilation and push for 2 or more hours, and the baby's head has not moved down (for whatever reason), it is called failure to descend and a cesarean section is performed. The reasons for failure of descent can be due to a large baby, an umbilical cord problem, deflexed head, CPD, etc.