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Can you explain labor with diagram

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Here is a complete explanation of Labor (Parturition) with textbook diagrams.

Labor (Parturition)

Labor is defined as regular uterine contractions that produce progressive cervical change, ultimately resulting in delivery of the baby and placenta. It is divided into 4 stages.

Hormonal Initiation of Labor

The fetal hypothalamus triggers a hormonal cascade:
  1. Fetal hypothalamus → corticotropin-releasing hormone (CRH)
  2. CRH → anterior pituitary → ACTH
  3. ACTH → adrenal cortex → cortisol
  4. Cortisol stimulates estrogen synthesis
  5. Estrogens increase myometrial contractility and stimulate release of oxytocin and prostaglandins
  6. Oxytocin (from posterior pituitary) drives peristaltic uterine smooth muscle contractions

The 4 Stages of Labor

The diagram below shows cervical dilation over time, with each stage labeled:
Stages of labor - cervical dilation graph
Fig. 176.1 - Rosen's Emergency Medicine: Stages of labor and delivery plotted as cervical dilation vs. time

Stage 1 - Cervical Stage (5-8 hours)

  • Begins: Onset of regular uterine contractions
  • Ends: Full cervical dilation (10 cm) and complete effacement
  • Divided into two phases:
PhaseCervical DilationCharacteristics
Latent phase0-3 cmSlow; irregular contractions; cervix softens and effaces
Active phase3-10 cmRapid dilation ~1.2 cm/hr (nulliparous), ~1.5 cm/hr (multiparous)
The image below shows the fetus in utero just before dilation begins, with the placenta, vagina, and anus labeled:
Fetus in uterus - Stage 1 start
The fetus in the uterus at the onset of labor - The Developing Human (Moore)

Stage 2 - Fetal Expulsion (20-54 minutes)

  • Begins: Full cervical dilation (10 cm)
  • Ends: Delivery of the infant
  • Average duration: 20 min (multiparous) to 54 min (nulliparous)
  • The fetus descends through the birth canal; the head typically presents first (vertex presentation)

Stage 3 - Placental Expulsion (~20 minutes)

  • Begins: Delivery of the infant
  • Ends: Delivery of the placenta
  • The uterus contracts, the placenta separates from the uterine wall, causing bleeding and hematoma formation
  • Usually complete within 10 minutes; intervention considered after 30 minutes
The image below shows placental separation with hematoma formation (Stage 3 - G):
Placental separation with hematoma - Stage 3
And the final expulsion of the placenta with a contracted uterus (Stage 3 - H):
Expelled placenta with contracted uterus - end of Stage 3
Figs. G and H from The Developing Human (Moore): placental separation and expulsion

Stage 4 - Recovery (1 hour postpartum)

  • The uterus continues to contract to prevent hemorrhage
  • Vital signs are monitored closely
  • This stage is not always listed in all classifications but is important clinically

True vs. False Labor (Braxton Hicks)

FeatureTrue LaborFalse Labor
Contraction rhythmRegularIrregular
IntervalsGradually shortenUnchanged
IntensityGradually increasesUnchanged
Discomfort locationBack AND abdomenLower abdomen only
Effect of sedationNo reliefUsually relieved
Cervical dilationYesNo

Key Terms

  • Effacement - thinning/shortening of the cervix (0% = thick, 100% = paper-thin)
  • Dilation - opening of the cervix (0-10 cm; full dilation = 10 cm)
  • Bloody show - expulsion of the cervical mucous plug at labor onset; slight dark-red bleeding mixed with mucus
  • Station - position of the fetal presenting part relative to the ischial spines
Sources: The Developing Human - Clinically Oriented Embryology (Moore), p. 369 | Rosen's Emergency Medicine, p. 3408 | Tintinalli's Emergency Medicine, p. 1944
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