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Fetal Heart Monitoring

General:​

  • Cardiotocography (CTG) = Non-stress test (NST).

  • The length of recorded fetal heart rate (FHR) taken is usually 10 minutes (the minimum baseline can be as short as 2 minutes).

  • CTG is reviewed in relation to mom’s contractions when in labor.

    • CTG can be used to monitor FHR during antenatal care from 28 weeks gestation.

​​​

  • FHR Baseline = a total of at least 2 min of FHR being around the level of a certain bpm + variabilities [because there are fluctuations (variabilities), the average is taken].

    • Don’t include accelerations, decelerations, & marked variabilities (>25 bpm)

    • Each box horizontally on CTG = 10 seconds, meaning each 6 boxes = 1 minute.

    • Each box vertically on CTG = 10 bpm.

    • Round it to nearest 5 bpm (e.g. FHR is 128 bpm you round it to 130 bpm)

    • If a total of 2 mins (12 boxes) of baseline can’t be seen -> baseline is indeterminate.

    • Changes in baseline = acceleration or deceleration length of ≥ 10 mins.

    • Normal range = 110 – 160 bpm

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  • Fetal tachycardia = FHR baseline > 160 bpm for at least 10 mins.

    • Causes:

      • FETAL (repetitive decelerations, fetal tachyarrhythmia, prematurity).

      • MATERNAL (infection, fever, medications (e.g. beta agonists, atropine, cocaine), maternal hyperthyroidism, placental abruption.

​​​

  • Fetal tachycardia = FHR baseline < 110 bpm for at least 10 mins.

    • Causes:

      • FETAL (rapid fetal descent, cord prolapse, placental abruption, congenital heart block which is associated with maternal lupus)

      • MATERNAL (hypotension, uterine rupture, tachysystole, Beta- adrenergic blockers, local anesthetic like paracervical block).

​

  • Variability = irregular fluctuations/change from the baseline in amplitude (peak-to- trough). It represents the interaction between the sympathetic and parasympathetic systems.

    • It’s not related to contractions, so this doesn’t include accelerations or decelerations.

    • Absent = amplitude undetectable.

    • Minimal = ≤ 5 bpm change from baseline, either as peak increases or trough/nadir decreases.

      • Causes:

        • Fetal sleep state (usually lasts from 20 mins to 1 hour).

        • Sedation of mom (e.g. with magnesium sulfate or opioids).

        • Fetal hypoxia or acidosis, esp. if it’s continuous with absent accelerations, abnormal scalp pH & not responding to resuscitation -> treat acidosis.

        • Maternal use of steroids.

    • Moderate = 6 – 25 bpm change from baseline.

    • Marked = > 25 bpm change from the baseline.

​

  • Acceleration = abrupt increase in FHR which is < 30 sec. (3 boxes) from onset to peak, lasting for less than 2 minutes

    • Peak is an increase in FHR by

      • ​10 bpm or more from baseline, for GA of <32 weeks.

      • 15 bpm or more from baseline, for GA of >32 weeks.

    • From onset to return to peak, accelerations take no more than 10-15 sec.

    • Prolonged acceleration = acceleration length of ≥ 2 mins but < 10 mins.

    • Cause: uterine contractions, fetal movement and scalp stimulation; this is always reassuring!

​

  • Deceleration = decrease in FHR associated with uterine contractions.

Each box horizontally

on CTG = 10 seconds,

meaning

each 6 boxes

= 1 minute

Each box vertically on

CTG = 10 bpm

Absence of variability

in FHR is highly

predictive

of fetal compromise,

while presence isn’t

always and indication

that the fetus is well

How to describe decelerations?

  • By the decrease in FHR

    1. Gradual = onset of deceleration to nadir is ≥ 30 sec.

    2. Abrupt = onset of deceleration to nadir (lowest point) is < 30 sec.

  • How many time it appears

    1. Intermittent = decelerations occur with < 50% of the contractions

    2. Recurrent = decelerations which occur with ≥ 50% of the uterine contractions in a 20 min duration. They require greater degree of surveillance.

Types of decelerations:

  1. Early = Gradual decrease in FHR nadir of which coincides with contraction peak (mirrors contractions). The only type that is NORMAL. Caused by head compression.

  2. Late = Gradual decrease in FHR nadir of which is delayed till after the onset of contraction. Caused by uteroplacental insufficiency and fetal hypoxia.

  3. Variable = abrupt decrease in FHR that’s variable in relation to contractions.

    1. It is caused by cord compression.

    2. Severity is graded by duration.

    3. If it lasts more than 60 seconds it is considered severe prolonged cord compression.

    4. Less than that is transient cord compression is not worrisome.

​

FHR Tracing Categories:

  • EFM Category I (normal)→ normal acid-base balance:

    • Baseline rate is between 110 – 160 bpm

    • Moderate baseline FHR variability (6 – 25 bpm from baseline)

    • No late or variable decelerations

    • Early decelerations may be present or absent

    • Accelerations may be present or absent

​

  • EFM Category II = indeterminate acid-base status→needs close surveillance:

    • For all patterns that aren’t category I or category III

​

  • EFM Category III (abnormal)→abnormal acid-base balance:

    • Absent Baseline FHR variability & any of the following:

      • Recurrent late decelerations

      • Recurrent variable decelerations

      • Bradycardia or sinusoidal pattern (regular & symmetrical oscillation

Refrences:

  1. Hacker N, Gambone J, Hobel C. Hacker and Moore's essentials of obstetrics and gynecology. Philadelphia, PA: Saunders/Elsevier; 2010. 5th Edition

  2. Uptodate.com. Intrapartum fetal heart rate assessment [Internet]. 2015 [cited 4 December 2015]. Available from: http://www.uptodate.com/contents/intrapartum-fetal-heart-rate- assessment?source=search_result&search=cardiotocography&selectedTitle=1~5

  3. Perifacts.eu. PeriFACTS [Internet]. 2015 [cited 4 December 2015]. Available from: http://perifacts.eu/cases/Case_681_Sinusoidal_Fetal_Heart_Rate_Patterns.php

  4. AlNouh B. Fetal Heart Monitoring. Lecture presented at; 2015; KSAUHS.

  5. Perinatology.com. Intrapartum Fetal Heart Rate Monitoring [Internet]. 2015 [cited 4 December 2015].

    Available from: http://perinatology.com/Fetal%20Monitoring/Intrapartum%20Monitoring.htm USMLE

  6. Step 2 CK. Obstetrics and Gynecology. 2014.

  7. Le T. First aid USMLE step 2 CK. New York: McGraw-Hill Medical; 2014.

Written by:        Abeer Khairi

Reviewed by:     Bayan Alzomaili

                          Amal Al Moamari

Format editor:    Reem AlQarni

                           Adel Yasky

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