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Anesthesia techniques: 1st stage labor

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

Stage I:

Latent phase

  • 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).


  1. 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 PubMed Link

Other References

  1. Abstract: Newborn and Maternal Fentanyl Levels at Cesarean Section by Eisele et al. Anesth Analg 61:179 Link