Phases of Labor

Obstetric Anesthesia

Labor is defined as progressive cervical dilatation in association with uterine contractions. Labor can be divided into the following stages:

Stage I: A) Latent phase 

  • Variable duration
  • Starts at onset of labor
  • Complete when the rate of cervical dilation increases (~ 3 cm)

B) Active phase (contractions every 2-3 mins, last 1 min, up to 70 mm Hg)

  1. acceleration phase

  2. phase of maximal slope

  3. deceleration phase

  4. Normal active labor should progress 1 cm/hr

  5. 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)