Fetal Heart Monitoring
General:
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Cardiotocography (CTG) = Non-stress test (NST).
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The length of recorded fetal heart rate (FHR) taken is usually 10 minutes (the minimum baseline can be as short as 2 minutes).
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CTG is reviewed in relation to mom’s contractions when in labor.
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CTG can be used to monitor FHR during antenatal care from 28 weeks gestation.
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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].
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Don’t include accelerations, decelerations, & marked variabilities (>25 bpm)
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Each box horizontally on CTG = 10 seconds, meaning each 6 boxes = 1 minute.
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Each box vertically on CTG = 10 bpm.
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Round it to nearest 5 bpm (e.g. FHR is 128 bpm you round it to 130 bpm)
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If a total of 2 mins (12 boxes) of baseline can’t be seen -> baseline is indeterminate.
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Changes in baseline = acceleration or deceleration length of ≥ 10 mins.
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Normal range = 110 – 160 bpm
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Fetal tachycardia = FHR baseline > 160 bpm for at least 10 mins.
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Causes:
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FETAL (repetitive decelerations, fetal tachyarrhythmia, prematurity).
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MATERNAL (infection, fever, medications (e.g. beta agonists, atropine, cocaine), maternal hyperthyroidism, placental abruption.
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Fetal tachycardia = FHR baseline < 110 bpm for at least 10 mins.
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Causes:
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FETAL (rapid fetal descent, cord prolapse, placental abruption, congenital heart block which is associated with maternal lupus)
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MATERNAL (hypotension, uterine rupture, tachysystole, Beta- adrenergic blockers, local anesthetic like paracervical block).
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Variability = irregular fluctuations/change from the baseline in amplitude (peak-to- trough). It represents the interaction between the sympathetic and parasympathetic systems.
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It’s not related to contractions, so this doesn’t include accelerations or decelerations.
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Absent = amplitude undetectable.
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Minimal = ≤ 5 bpm change from baseline, either as peak increases or trough/nadir decreases.
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Causes:
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Fetal sleep state (usually lasts from 20 mins to 1 hour).
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Sedation of mom (e.g. with magnesium sulfate or opioids).
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Fetal hypoxia or acidosis, esp. if it’s continuous with absent accelerations, abnormal scalp pH & not responding to resuscitation -> treat acidosis.
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Maternal use of steroids.
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Moderate = 6 – 25 bpm change from baseline.
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Marked = > 25 bpm change from the baseline.
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Acceleration = abrupt increase in FHR which is < 30 sec. (3 boxes) from onset to peak, lasting for less than 2 minutes
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Peak is an increase in FHR by
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10 bpm or more from baseline, for GA of <32 weeks.
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15 bpm or more from baseline, for GA of >32 weeks.
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From onset to return to peak, accelerations take no more than 10-15 sec.
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Prolonged acceleration = acceleration length of ≥ 2 mins but < 10 mins.
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Cause: uterine contractions, fetal movement and scalp stimulation; this is always reassuring!
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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?
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By the decrease in FHR
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Gradual = onset of deceleration to nadir is ≥ 30 sec.
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Abrupt = onset of deceleration to nadir (lowest point) is < 30 sec.
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How many time it appears
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Intermittent = decelerations occur with < 50% of the contractions
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Recurrent = decelerations which occur with ≥ 50% of the uterine contractions in a 20 min duration. They require greater degree of surveillance.
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Types of decelerations:
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Early = Gradual decrease in FHR nadir of which coincides with contraction peak (mirrors contractions). The only type that is NORMAL. Caused by head compression.
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Late = Gradual decrease in FHR nadir of which is delayed till after the onset of contraction. Caused by uteroplacental insufficiency and fetal hypoxia.
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Variable = abrupt decrease in FHR that’s variable in relation to contractions.
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It is caused by cord compression.
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Severity is graded by duration.
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If it lasts more than 60 seconds it is considered severe prolonged cord compression.
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Less than that is transient cord compression is not worrisome.
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FHR Tracing Categories:
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EFM Category I (normal)→ normal acid-base balance:
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Baseline rate is between 110 – 160 bpm
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Moderate baseline FHR variability (6 – 25 bpm from baseline)
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No late or variable decelerations
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Early decelerations may be present or absent
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Accelerations may be present or absent
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EFM Category II = indeterminate acid-base status→needs close surveillance:
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For all patterns that aren’t category I or category III
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EFM Category III (abnormal)→abnormal acid-base balance:
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Absent Baseline FHR variability & any of the following:
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Recurrent late decelerations
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Recurrent variable decelerations
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Bradycardia or sinusoidal pattern (regular & symmetrical oscillation
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Refrences:
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Hacker N, Gambone J, Hobel C. Hacker and Moore's essentials of obstetrics and gynecology. Philadelphia, PA: Saunders/Elsevier; 2010. 5th Edition
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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
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Perifacts.eu. PeriFACTS [Internet]. 2015 [cited 4 December 2015]. Available from: http://perifacts.eu/cases/Case_681_Sinusoidal_Fetal_Heart_Rate_Patterns.php
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AlNouh B. Fetal Heart Monitoring. Lecture presented at; 2015; KSAUHS.
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Perinatology.com. Intrapartum Fetal Heart Rate Monitoring [Internet]. 2015 [cited 4 December 2015].
Available from: http://perinatology.com/Fetal%20Monitoring/Intrapartum%20Monitoring.htm USMLE
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Step 2 CK. Obstetrics and Gynecology. 2014.
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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