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Understanding Labor and Childbirth Mechanics

Apr 23, 2025

Lecture 6: Labor and Partition (Childbirth)

Overview of Labor

  • Labor Initiation: Begins when progesterone's inhibition is overcome by rising estrogen levels.
    • Progesterone: Inhibits uterine contraction, maintains uterine lining.
    • Estrogen: Stimulated by placenta converting fetal anterior pituitary DHEA, leading to uterine contractions as its levels rise.
  • Hormones Involved:
    • Progesterone: Decreases prior to labor.
    • Estrogens, Prostaglandins, Oxytocin, Relaxin: Involved in labor initiation and progression.

Mechanism of Labor

  • Uterine Contraction: Forces fetal head into cervix, activating stretch receptors.
    • Oxytocin Release: Due to activated stretch receptors, enhancing contractions in a positive feedback loop.

True vs. False Labor

  • True Labor:
    • Regular, painful uterine contractions.
    • Pain localized to the back.
    • Cervical dilation and bloody mucus discharge.
  • False Labor (Braxton Hicks Contractions):
    • Irregular pain without cervical dilation.

Stages of Labor

  1. Dilation
    • Duration: 6 to 12 hours.
    • Features: Regular uterine contractions, amniotic sac rupture ("water breaking"), cervix dilates to ~10 cm.
  2. Expulsion
    • Duration: 10 minutes to several hours.
    • Action: Baby moves through birth canal.
  3. Placental (Afterbirth)
    • Duration: ~30 minutes.
    • Occurrence: Placenta is expelled.
    • Nursing helps to expedite placental expulsion.

Complications in Labor

  • Dystocia: Difficult labor due to factors like fetal position or birth canal size.
    • Cesarean Section (C-section): May be necessary for difficult births; involves a horizontal incision in the lower abdomen.
    • Breech Presentation: Fetus positioned buttocks or feet first instead of head first.

Post-Labor Period

  • Puerperium: 6-week period post-delivery where reproductive organs and maternal physiology return to pre-pregnancy state.
    • Involution: Uterus shrinking process.
    • Lochia: Uterine discharge of blood and serous fluid for 2-4 weeks.

Lecture Objectives

  • Differentiate between labor and partition (childbirth).
  • Recognize differences between true and false labor.
  • Identify signs of labor.
  • Describe the three stages of labor.
  • Define terms: Dystocia, Breech Presentation, Puerperium, Involution, Lochia, C-section.

Full transcript