Intrapartum fetal heart rate monitoring

Cardiotocography aka electronic fetal monitor, monitors the fetal heartbeat and uterine contractions during pregnancy – main purpose is for peripartum fetal heart rate monitoring.

Besides accelerations, there are 3 types of decelerations that need to be differentiated as they have different etiologies, prognosis and managements – Early, Late and Variable.

Early Deceleration: 

Relationship to contraction:

  1. Symmetric to contraction
  2. Nadir of deceleration corresponds to peak of contraction
  3. Gradual onset(>30 seconds from onset to nadir)

Etiologies:

  1. Fetal head compression
  2. May be normal

Late Deceleration: 

Relationship to contraction:

  1. Almost just as symmetric but delayed compared to contraction
  2. Nadir of deceleration occurs obviously after peak of contraction
  3. Gradual onset

Etiologies:

  1. Uteroplacental insufficiency: A suboptimally functioning placenta which causes transient fetal hypoxemia which is reflected by late decelerations – placental calcifications may be apparent.

Variable Decelration:

Image result for tocometer variable decelerations

Relationship to contraction:

  1. Variable relationship compared to contractions
  2. Abrupt onset(main way of differentiating between early decelerations and recurrent variable decelerations)
  3. Decrease > 15/min and 15 sec < duration < 2min

Classification

  1. Intermittent: associated with <50% of contractions – well tolerated by fetus and typically do not cause hypoxia
  2. Recurrent: associated with >50% of contractions and may mimic early decelerations – require treatment due to possibility of fetal acidosis

Etiologies

  1. Cord compression: Maternal repositioning followed by amnioinfusion is failure to improve
  2. Oligohydramnios
  3. Cord prolapse: Can be seen at cervix

 

Q: 12037, 8962

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