Understanding the Stages of Labor

Sep 19, 2024

Stages of Labor

Overview

  • Labor refers to the delivery process of a baby.
  • Occurs between 37-42 weeks when the fetus is full term.
  • Preterm labor: Occurs before 37 weeks.
  • Divided into three stages:
    1. Cervical dilation.
    2. Delivery of the fetus.
    3. Delivery of the placenta.

Initiation of Labor

  • Cervix stretches at the end of the third trimester.
  • Brain releases oxytocin, stimulating uterine contractions.
  • Placenta releases prostaglandins, also stimulating contractions.
  • Positive feedback loop created through cervical stretching and contractions.
  • Braxton Hicks contractions: Mild and irregular, known as false labor pains.
  • Indicators of approaching labor:
    • "Show of labor": Discharge as mucus plug falls due to decreased estrogen.
    • Rupture of amniotic membranes.

Stage 1: Cervical Dilation

  • Process where the cervix opens up to 10 cm.
  • Divided into:
    • Latent Phase: Cervix dilates slowly up to 4 cm, irregular contractions.
    • Active Phase: Regular, painful contractions; cervix becomes fully dilated.
    • Effacement: Cervix becomes thinner.
    • Dilation: Cervix opens.
    • Progression slower in nulliparous women (1 cm/hr) compared to multiparous women (2 cm/hr).

Stage 2: Delivery of the Fetus

  • From full dilation to delivery of the baby.
  • Divided into:
    • Passive Phase: Descent of the fetal head.
    • Active Phase: Mother actively pushes.
  • Determined by the "Three P's":
    • Powers: Strength of uterine contractions (4-5 in 10 minutes).
    • Passage: Maternal pelvis anatomy, consisting of inlet, mid cavity, and outlet with specific diameters.
    • Passenger: Fetal characteristics (head size, attitude, position).
  • Fetal Head:
    • Bones: Frontal, parietal, occipital.
    • Sutures and fontanelles (anterior/posterior) allow compression (molding) and swelling (caput).
  • Fetal Attitude and Position:
    • Ideal: Head completely flexed, vertex presentation (9.5 cm diameter).
    • Position changes during delivery to accommodate pelvis dimensions.
    • Rotation occurs to fit largest pelvis diameters.
  • Delivery involves flexion, rotation, extension, and restitution (for shoulder delivery).

Stage 3: Delivery of the Placenta

  • Lasts about 15 minutes.
  • Normal blood loss is up to 500 mL.

Conclusion

  • Labor is a complex process involving multiple stages and physiological changes.
  • Understanding these stages helps in managing labor effectively.