Occurs in 0.2-3% of all births
Anterior<unk>  becomes impacted against maternal pubic symphysis
Pre-labor
Previous<unk> 
Macrosomia
Diabetes mellitus
Maternal BMI > 30
Induction of labor
Advanced maternal age
Short maternal stature
Small maternal pelvis
Significant post-dates delivery (>42 weeks gestation)
Intrapartum
Prolonged first or second stage
Oxytocin augmentation
Failure to restitute
Failure of<unk>  rotation on descent
Assisted vaginal delivery
Prolonged head to body delivery time >60 seconds
Previous<unk> 
Macrosomia
Diabetes mellitus
Maternal BMI > 30
Induction of labor
Advanced maternal age
Short maternal stature
Small maternal pelvis
Significant post-dates delivery (>42 weeks gestation)
Prolonged first or second stage
Oxytocin augmentation
Failure to restitute
Failure of<unk>  rotation on descent
Assisted vaginal delivery
Prolonged head to body delivery time >60 seconds
Prolonged head to body delivery time >60 seconds
Shoulder dystocia
Emergent delivery
Cervical injury 
Umbilical cord prolapse
Infant scalp hematoma
Breech delivery
Preterm labor
Perimortem cesarean delivery