OB/GYN
Antepartum Fetal Surveillance
OB/GYN

Antepartum Fetal Surveillance

NST, BPP, CST, Doppler; oligohydramnios, post-term, IUGR.

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◆Non-stress test (NST)

  • •First-line for decreased fetal movement
  • •Reactive (normal): ≥2 accelerations of ≥15 bpm × 15 sec in 20 minutes
  • •Nonreactive → proceed to BPP
  • •Acceleration confirms fetal autonomic nervous system intact

◆Biophysical profile (BPP)

  • •5 components × 2 points = 10 max
  • •NST (reactive)
  • •Fetal breathing movements
  • •Gross body movements
  • •Fetal tone
  • •Amniotic fluid volume
  • •8–10: reassuring; 6: equivocal; ≤4: deliver

◆Contraction stress test (CST)

  • •If BPP equivocal
  • •Late decelerations → uteroplacental insufficiency

◆Umbilical artery Doppler

  • •End-diastolic flow: normal forward
  • •Reduced flow → placental insufficiency
  • •Absent or REVERSED end-diastolic flow → severe insufficiency → consider delivery

◆Oligohydramnios

  • •Amniotic fluid index (AFI) <5 cm or single deepest pocket <2 cm
  • •Causes: uteroplacental insufficiency (HTN), renal agenesis (Potter), NSAIDs (indomethacin), post-term, PROM
  • •Complications: cord compression → variable decels, meconium aspiration
  • •Management: depends on cause; deliver if term and unresolving

◆Polyhydramnios

  • •AFI >24 cm
  • •Causes: fetal swallowing/GI obstruction (esophageal/duodenal atresia, TEF), GDM, multiple gestation, anencephaly, fetal anemia
  • •Complications: preterm labor, malpresentation, cord prolapse

◆IUGR / Fetal growth restriction

  • •Symmetric (early insult): TORCH, chromosomal, drugs/alcohol — entire body small
  • •Asymmetric (late insult): uteroplacental insufficiency — brain-sparing, smaller abdomen/liver
  • •Surveillance: serial growth US, Doppler, BPP/NST

◆Post-term pregnancy (>42 weeks)

  • •Placental aging → ↓ perfusion → oligohydramnios + fetal distress
  • •Risks: macrosomia, meconium aspiration, stillbirth
  • •>41 weeks: increased monitoring
  • •>42 weeks: INDUCE labor

◆Fetal heart rate patterns

  • •Normal baseline: 110–160 bpm
  • •Moderate variability (6–25 bpm): reassuring
  • •Accelerations: reassuring (autonomic intact)
  • •Early decels: head compression — benign
  • •Late decels: uteroplacental insufficiency — concerning (deliver if recurrent)
  • •Variable decels: cord compression — amnioinfusion if recurrent
  • •Category I: normal; Category II: indeterminate; Category III: abnormal (sinusoidal, absent variability + decels) → emergent delivery

High-yield pearls

  • ◆Decreased fetal movement → NST first
  • ◆NST nonreactive → BPP
  • ◆Late decels = uteroplacental insufficiency
  • ◆Variable decels = cord compression
  • ◆Sinusoidal pattern = severe fetal anemia (consider Kleihauer-Betke)
  • ◆Oligohydramnios → renal/placental; Polyhydramnios → swallowing/obstruction
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