Normal labor and delivery

Station (Obstetrics)

• Definition: Fetal head level relative to ischial spines (IS).
• Station Scale:
  • Station 0: Fetal head at IS = Engaged (biparietal diameter passed pelvic inlet).
  • Negative (-5 to -1 cm): Above IS (unengaged).
  • Positive (+1 to +5 cm): Below IS (+3 to +5 = crowning).
• High-Yield Management Rules:
  • AROM contraindicated if station < 0: Risk of umbilical cord prolapse.
  • Operative Vaginal Delivery (Forceps/Vacuum): Requires station ≥ 0 (strictly contraindicated if unengaged).
  • Caput Succedaneum: Soft tissue edema crosses suture lines; can misrepresent station. Always palpate bony skull, not soft tissue.
  • Failure to engage + adequate contractions (≥ 200 MVUs) = CPD $\to$ Tx: C-section.

Intrapartum fetal monitoring

• Fetal Heart Rate (FHR) Basics:
  • Baseline: Normal 110–160 bpm.
    • Tachycardia (>160 bpm): Most commonly intraamniotic infection (chorioamnionitis); also maternal fever, beta-agonists, fetal anemia.
    • Bradycardia (<110 bpm): Maternal hypotension (post-epidural), cord prolapse/compression, maternal SLE (anti-SSA/Ro $\to$ congenital heart block).
  • Moderate variability (6–25 bpm): Normal, rules out fetal acidemia.
  • Minimal/Absent variability: Fetal sleep cycle (normal), opioids/sedatives, or fetal hypoxia/acidemia. c
  • Sinusoidal pattern: Smooth wave-like trace = Severe fetal anemia (Rh alloimmunization, vasa previa) → Emergency C-section. c
    • Profound tissue hypoxia ($\text{Hb}<7\text{ g/dL}$) causes ischemic disruption of the medullary autonomic centers $\to$ failure of sympathetic/parasympathetic balance $\to$ undamped oscillating sine wave.
• Deceleration Patterns (VEAL CHOP):
  • Variable = Cord compression (abrupt drop, variable timing) → Maternal repositioning; if persistent → Amnioinfusion. c
    • Variable: Cord can be compressed intermittently by fetal limbs, body turns, or oligohydramnios; compression does not rely purely on peak contraction intensity.
  • Early = Head compression (nadir at contraction peak) → Benign, continue monitoring.
    • Contraction compresses fetal skull $\to$ transient ↑ ICP $\to$ central vagal reflex slows SA node.
  • Accelerations = Oxygenated (≥15 bpm for ≥15 sec if ≥32 wks) → Normal, rules out acidemia.
    • Fetal movement $\to$ intact brainstem triggers sympathetic burst $\to$ transient $\uparrow$ HR.
  • Late = Placental insufficiency (nadir after contraction peak) → Intrauterine resuscitation.
    • Contraction cuts off maternal blood flow $\to$ compromised placenta drops fetal ${\text{pO}}_2$ $\to$ chemoreceptors trigger vasoconstriction $\to$ HTN causes secondary vagal reflex.
    • Timing: Nadir lags after peak because fetal ${\text{pO}}_2$ takes time to fall below threshold and re-equilibrate. (Indicates hypoxemia).
• Three-Tier Classification:
  • Category I: Normal baseline + Moderate variability + No late/variable decels → Routine care.
  • Category II: Indeterminate (e.g., minimal variability, late decels w/ mod variability) → Intrauterine resuscitation + Fetal scalp stimulation (acceleration rules out acidemia).
  • Category III: Absent variability + recurrent late/variable decels/bradycardia OR Sinusoidal → Emergency delivery (C-section/Operative delivery).
• Intrauterine Resuscitation Protocol (Next step for Cat II/III or Late Decels):
  • Left lateral position (relieves IVC compression).
  • O2 mask + IV fluid bolus (treats maternal hypotension).
  • Discontinue Oxytocin immediately.
  • Terbutaline (tocolytic) if uterine tachysystole (>5 contractions in 10 min).
• Fetal Scalp Electrode (FSE) Contraindications:
  • Maternal HIV, HCV, or active genital HSV (risk of vertical transmission).