Cardiotocography (CTG): Important points to remember

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Introduction:

  • Cardiotocography (CTG) is used to monitor fetal well-being and allow early detection of fetal distress
  • It is most commonly used in the third trimester
  • The device used in cardiotocography is known as a cardiotocograph or electronic fetal monitor (EFM)
  • It involves the placing two transducers onto the abdomen of a pregnant woman:
    • One transducer records the fetal heart rate using ultrasound
    • The other transducer monitors the contractions of the uterus.

Terminologies:

  • Baseline heart rate: 110-160 bpm
  • Bradycardia: <110 bpm
  • Tachycardia: >160 bpm
  • Normal beat to beat variability: 5-25 bpm.

Important types of CTG to identify in exam

  1. Early deceleration:
    • Early decelerations are caused by fetal head compression during uterine contraction, resulting in vagal stimulation and slowing of the heart rate
    • These decelerations are not associated with fetal distress and thus are reassuring
    • This type of deceleration has a uniform shape, with a slow onset that coincides with the start of the contraction and a slow return to the baseline that coincides with the end of the contraction
    • Thus, it has the characteristic mirror image of the contraction.
  2. Late deceleration:
    • A late deceleration is a fall in the FHR, beginning at or after the peak of the uterine contraction and returning to baseline only after the contraction has ended
    • Late decelerations are associated with uteroplacental insufficiency and always considered potentially ominous.
  3. Variable deceleration:
    • Variable decelerations are shown by an acute fall in the FHR with a rapid downslope and a variable recovery phase
    • Variable decelerations are caused by compression of the umbilical cord
    • They are the most commonly encountered patterns during labor
    • Associated with PROM and decreased amniotic fluid volume.
  4. Sinusoidal pattern:
    • It is a regular, smooth, undulating form typical of a sine wave
    • Stable baseline heart rate of 120-160 bpm and absent beat-to-beat variability
    • Indicates severe fetal anemia or severe hypoxia.

Summary:

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