Most pregnant women have an image of how they believe their delivery will go. However, a vaginal birth isn't always possible – or wanted. According to the Centers for Disease Control and Prevention, approximately 30 percent of live births in 2005 were delivered by Cesarean section. Some were due to emergency situations and others were planned.

There are many reasons for unplanned Cesarean sections. The most common scenarios are fetal distress and a failure to progress, with many other less common reasons.

Fetal Distress
Fetal distress can occur any time during labor and usually results in an emergency C-section.

"We monitor the heart rate tracing of the fetus when a woman is in labor and look for a pattern that we consider 'reassuring,'" says Dr. Allison Hunt, an OB/GYN at Methodist Hospital, Houston, Texas. "There are certain patterns on the fetal heart rate tracing that we consider 'non-reassuring,' which causes concern that the fetus may not be getting enough blood flow through the placenta and therefore not enough oxygen. If the fetus does not get enough oxygen for a significant period of time, the end result could be brain injury."

Failure to Progress
The primary reason for unplanned C-section is a failure to progress in labor, sometimes called labor dystocia or cephalopelvic disproportion (when the baby is too large to fit through the mother's pelvis).

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