Labor is defined as progressive cervical dilatation in association with uterine contractions. Labor can be divided into the following stages:
- Variable duration
- Starts at onset of labor
- Complete when the rate of cervical dilation increases (~ 3 cm)
Active phase (contractions every 2-3 mins, last 1 min, up to 70 mm Hg)
- acceleration phase
- phase of maximal slope
- deceleration phase
Normal active labor should progress 1 cm/hr Most common measure of uterine activity is the Montevideo unit (avg intensity frequency per 10 minutes)
Stage II: interval between maximal dilation and delivery (20-120 mins)
Stage III: placental delivery (5-20 mins)
In the first stage of labor, pain travels via sympathetic nerve fibers (going through the inferior hypogastric plexus on the way to the sympathetic chain) that originate from the T10-L1 segments of the spinal cord (referred to the back as well as abdominal wall).
Common techniques include systemic medication administration (single doses of < 1 ucg/kg or lower appear to have no effects on fetal APGAR scores).
- Michael A Frölich, David J Burchfield, Tammy Y Euliano, Donald Caton A single dose of fentanyl and midazolam prior to Cesarean section have no adverse neonatal effects. Can J Anaesth: 2006, 53(1);79-85