Obstetrics Book

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Fetal Station

Aka: Fetal Station, Fetal Descent
  1. Definition: Fetal Station
    1. Zero Station Notation (presenting part level)
      1. Presenting part in relation to ischial spines
      2. Reported in centimeters from ischial spines
      3. Negative numbers are behind the ischial spines
    2. Engagement
      1. Refers to presenting part meeting pelvic floor
      2. Occurs at 0 station
  2. Step 1: Fetal Descent
    1. Fetal head position on abdominal palpation
      1. Head fixed: 3/5 palpable abdominally
      2. Head engaged: 2/5 palpable abdominally
    2. Fetal Heart Tones change position (towards Pelvis)
  3. Step 2: Fetal neck flexion
    1. Partial flexion prior to labor (natural fetal tone)
    2. Flexion of Cervical Spine (chin to chest) with descent
      1. Occiput Anterior
        1. Presenting diameter changes from occipitofrontal
          1. Nasal bridge to Posterior Fontanelle
        2. Transforms into smaller suboccipitobregmatic
          1. Posterior Fontanelle to sub-occiput
      2. Occiput Posterior
        1. Incomplete flexion
        2. Larger presenting diameter
        3. Prolonged labor
  4. Step 3: Internal Rotation
    1. Occiput Anterior
      1. Occiput initially transverse or oblique
      2. Occiput rotates anteriorly towards symphysis pubis
      3. Occurs as presenting part reaches pelvic floor
        1. Engagement (ischial spines: Zero station)
    2. Occiput Posterior
      1. Possibility 1
        1. Head rotates posteriorly
        2. Occiput turns to hollow of Sacrum
      2. Possibility 2 (75% of cases)
        1. Occiput Posterior converts to Occiput Anterior
        2. Fetus Rotates 90 degrees
  5. Step 4: Extension
    1. Occiput Anterior
      1. Head extends to meet the vaginal outlet
      2. Oriented upward and forward
      3. Crowning occurs (+5 Station)
    2. Occiput Posterior
      1. Combination of flexion and extension
  6. Step 5: External Rotation (Head delivered)
    1. Delivered head returns to position at engagement
    2. Head aligns with back and Shoulders
  7. Step 6: Expulsion (body delivered)

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