Fetal Monitoring Glossary

Baseline Characteristics- Fetal Heart Rate And Variability

Periodic Changes- Accelerations And Decelerations Which Occur In Association With Contractions

Non-periodic Changes- Accelerations And Decelerations Which Occur Without Any Relationship To Contractions

Fetal Heart Rate Pattern- Fetal Heart Rate, Variability, Accelerations And Decelerations

Short-term Variability- The Fetal Heart Rate Per Minute Changes Calculated From One Beat Of The Heart To The Next

Long-term Variability- The Fluctuation Of The Fetal Heart Rate Over The Course Of One Minute

• Average-5-15bpm
• Increased-more Than 15 Bpm
• Decreased-less Than 5 Bpm
• Absent-less Than 2 Bpm

Tachycardia- Heart Rate Above 160 Bpm For Ten Minutes Or More

Bradycardia-heart Rate Less Than 120 Bpm For More Than Ten Minutes

Variability- The Change In The Fetal Heart Rate Baseline Due To The Interplay Of The Sympathetic And Parasympathetic Branches Of The Autonomic Nervous System

"Shoulders"-variable Accelerations Before And After Variable Decelerations

Early Decelerations

• Shape-uniform
  • Mirror Image
• Onset-with Onset Of Contraction
  • Lag Time Less Than 20 Seconds
• Duration-length Of Contraction
• Amplitude-proportional With Contraction
• Repetitive
• Proposed Mechanism-head Compression
• Common During Second Stage
• Common In Primigravidas
• Unaffected By Position Change Or Oxygen Administration
• Not Associated With Alterations In Baseline Heart Rate Or Acid-base Balance
• Benign Pattern

Variable Decelerations

• Shape-variable
• Onset-variable
  • Lag Time Variable
• Amplitude-variable
  • Usually Unrelated To Amplitude And Duration Of Contraction
• Need Not Be Repetitive
• Proposed Mechanism-umbilical Cord Compression
• Most Common Pattern Observed
• High Incidence With Fetuses With Nuchal Cord
  • Short Cord
  • Prolapsed Cord
• In Majority Of Cases, No Obvious Explanation Is Found
• More Common When Membranes Are Ruptured
• Decelerations Corrected Or Precipitated By
• Manipulations (Vag Exam, Maternal Position Change, Scalp Sampling)
• With Good Fetal Reserve Moderate To Severe Variables May Be Accompanied By Erratic Rebound Acceleration And Average To Increased Baseline Variability
• In Compromised Fetus
  • "Shoulders" (Variable Accelerations) Disappear
  • Rising Heart Rate And Diminishing Variability
  • "Peaked" Shoulder Follow Deceleration
  • "Overshoots" (Recurrent Rebound Accelerations) Appear
  • Judge Severity Of Deceleration Not By Duration Or Amplitude, But By Impact

On Baseline Rate And Variability

• Obtain Ph Sample Between Decelerations To Determine Impact On Fetus

Late Decelerations

• Shape-uniform
• Onset-late In Contraction
  • Lag Time Greater Than 20 Seconds
• Duration-proportional To Duration Of Contraction
• Amplitude-proportional To Amplitude Of Contraction
• Repetitive
• Proposed Mechanism-diminished Uterine Blood Flow With Contraction
• Associated With Obstetrical/Anesthetic Procedures
  • Supine Hypotension
  • Epidural Anesthesia
  • Spinal Anesthesia
  • Excessive Uterine Activity
• Associated With Placental Insufficiency
  • Intrauterine Growth Retardation
  • Hypertension
  • HELLP Syndrome
• Position Change May Improve Pattern If Related To Supine Hypotension
• Oxygen Administration May Decrease Or Abolish Pattern
  • Unclear Whether Oxygen Administration Improves Fetal Acid-base Abnormalities
• Diminished Variability
• Tachycardia Common
• If Deceleration Present For More Than 20 Minutes, Acidosis Usually Found
• Acidosis Proportional To Severity And Duration Of Decelerations
• Acidosis Less With Good Variability Than With Poor Variability

• Onset-abrupt
• Amplitude-less Than 30 Bpm
• Duration-at Least 2 Minutes
• Proposed Mechanism-uncertain
  • Probably Reflex (Vagal) In Origin
• Can Cause Hypoxia If Prolonged
• Can Be Caused By
  • Uterine Hypertonus
  • Manipulation
    • Vag Exam
    • Scalp Sampling
    • Position Change
  • Drugs
    • Especially With Uterine Contractions
• Occur Most Commonly In The Second Stage
• Majority Of Babies With These Decelerations Will Be Delivered In Good Condition
• Recovery Usually Occurs If Normal Variability Present Or Variability Present

• Anticipate Intervention If Previous Pattern Abnormal
• Anticipate Intervention If Deceleration Persists Beyond 3 Minutes
• Acid-base Balance Changes
• Delivery Not Necessarily The Best Course Of Management, Despite The Fact

Combined Decelerations

• Combination Of Two Patterns
  • Early/Late
  • Early/Variable
  • Variable/Late
• Unusual Patterns
• Treat According To Worst Pattern

• Spontaneous
  • Seen With Fetal Movement Or Stimulation
  • Represents Integrative Response Of Fetal CNS
  • This Is The Basis Of Reactive NST
  • Benign Response
• Variable
  • Don't Reflect Shape Of Contraction
  • "Shoulders" On Variable Decelerations
  • As A Feature Of "Increased Variability" With Contractions
  • Usually Associated With Good Variability
  • Apparently Benign Response
• Rebound Accelerations (Overshoot)
  • Uniform Accelerations Following Variable Decelerations
  • Smooth Baseline
  • Can Also Be Seen In Immature Fetus
  • Usually Longer Than 12 Seconds
  • Follows Variable Deceleration Regardless Of Amplitude
  • Ominous Commentary On Variable Deceleration
• Accelerations Associated With Variable Decelerations "Shoulders" "Overshoot" Occurrence Precedes Follows And/Or Variable Follows Decelerations Variable Consistent May Vary Recurrent From Contraction To Contraction Duration Usually Less Than 12 Sec More Than 12 Seconds Baseline Usually Average Absent Variability Sometimes Increased Fetal Condition Usually Good Severely Asphyxiated Prematurity Immaturity Proposed Mechanism Minor Degree Impairment Of Slowly Developing Vagally Mediated Umbilical Cord Control Mechanism Compression Interaction Of Sympathetic And Parasympathetic Systems Drug Effects On Fetal Heart

• Tranquilizers/Sedatives
  • Decreased Baseline Variability
  • If Fetus Is Hypoxic Will Develop Decelerations

• Beta-andrenergic Blockers (Proprandolol,Etc.)
  • Decrease Rate
  • Decrease Variability

• Beta-adrenergic Stimulants (Terbutaline, Ritodrine)
  • Decrease Variability
  • Increase Rate
  • Beat-to-beat Arythmia
  • Similar Changes In Mother

• Ephedrine
  • May Increase Baseline Rate
  • Increase Variability(Saltatory Pattern)
  • Corrects Hypotensions

• Oxytocin
  • Fetus Determines Excessive Activity
  • Effect Of Fetus Secondary To Effect On Uterine Blood Flow

• Local Anesthetics
  • Drugs Appear In Fetus-poorly Metabolized
  • Direct Cardiac Toxicity With Massive Dose
  • Maternal Convulsions After In Injection
  • Maternal Hypotension After Epidural
  • Drugs Appear In Fetal Circulation Irregardless Of Injection Site

  Fetal Monitoring Upon Admission

• Initial Assessment-normal Criteria
  • Stable Heart Rate
  • Average Variability-accelerations
  • Absent Decelerations With Contractions
• If All Criteria Met- Discontinue
• If Abnormal- Continue
• Remonitor
  • Unusual Contractions, Pain
  • Rupture Of Membranes
  • Transition
  • Second Stage
  • Medication
  • Stimulation

  Principles Of EFM Interpretation

• Baseline Variability Reflects Fetal Reserve
• Variable Decels-Umbilical Cord Compression
• Late Decels-Placental Insufficiency
• Early Decels-Head Compression
• Decels That Return Slowly To Baseline But Don't Exceed Previous Baseline
• Don't Represent Asphyxia (In Fetus With Normal Variability And No Tachycardia) Treatment

• Avoid The Cause Or Treat The Cause Which Is Usually Impaired Uterine Or
• Umbilical Blood Flow
  • Improve Uterine Blood Flow
  • Avoid Supine Position
  • Avoid Drugs
  • Minimize Maternal Hypotension
• Improve Umbilical Blood Flow
  • Change Maternal Position
    • Hands And Knees
    • Lateral
    • Knee Chest
  • Ve-check For Cord Prolapse
    • Elevate Presenting Part
  • Correct Oligohydramnios-amniofusion
  • Stop Pushing
  • Tocolysis
• Increase Maternal And Fetal Oxygenation
• Restrict Potentially Compromising Techniques
  • Regional Anesthesia
  • Oxytocin
• Treatment Of Variables
  • Improve Umbilical Blood Flow
• Treatment Of Late Decels
  • Improve Uterine Blood Flow
  • Oxygen-remove After Recovery
• Treatment Of Prolonged Decels
  • Same As For Variables
  • If Good Variability- Anticipate Recovery
  • If Poor Variability-consider Intervention If Not Approving In 4 Min

  Fetus

• Dependent On Placental Exchange For Nutrition And Oxygenation
• Labor Reduces Placental Exchange
• Direct Correlation Between Intensity, Duration And Frequency Of Contractions And Reduction In Placental Exchange
• Fetus Adapts To Stress Through Its Cardiovascular And Autonomic Nervous System Parasympathetic System
• Influences Fetal Heart Rate Between Consecutive Heart Beats (Beat-to-beat Or Short-term Variability
• Vagus Nerve Is Primary Nerve Of Parasympathetic System
• System Increases As Fetus Matures Sympathetic System
• Sympathetic Nerve Endings Widely Distributed In Fetal Heart At Term
• Release Norepinephrine If Stimulated
• Increases Heart Rates And Vigor Of Contractions
• Sympathetic And Parasympathetic Systems Interplay To Affect Fetal Heart Rate And Variability
• Balance Between The Two Systems Altered By
• Change In Intrauterine Environment
• Fetal Movement
• External Stimuli
• Change In Po2 And Pco2 Concentrations Fetal Cardiac Output
• Fetal Cardiac Output Is Almost Directly Proportional To The Heart Rate
• Cardiac Output Decreases If Heart Rate Is Too Low Or Too High Placenta
• Placental Transfer Is Dependent On Placental Size And Rate Of Blood Flow In Maternal And Fetal Sides Of Placenta
• Maternal Nutrition Is An Important Determinant In Placental Size
• Placental Growth Also Affected By Hypertension Or Vascular Disease
• Role Of Placenta In Labor Is To Maintain Fetal Homeostasis
• Placental Function Can Be Chronically Impaired By
• Hypertension
• Insulin Dependent Diabetes Mellitus
• Rh Sensitization
• IUGR With Depleted Glycogen Stores
• Presence Of Severe Anomalies Umbilical Blood Flow
• Constriction Of Cord Vessels Associated With
• Severe Maternal Hypoxemia
• Acute Or Chronic Uteroplacental Insufficiency
• Maternal Anxiety And Stress With An Increase In The Transfer Of Catecholamines
• Vasoconstriction Due To Prostaglandins Uterine Blood Flow
• Blood Flow Is Acutely Reduced In The Presence Of
• Supine Hypotension
• Regional Anesthesia (Spinal And Epidural)
• Hemorrhage
• Blood Flow Also Reduced By
• Contractions
• Pre-eclampsia
• Hypotension And Reduction In Maternal Cardiac Output
• Arterial Vasoconstriction
• Endogenous Source Catecholamines
• Exogenous Source Smoking
• Diabetes Mellitus
• Renal Disease
• Sedatives And Analgesics Contractions
• Lowest Pressure Between Contractions Is Resting Tone
• During Pregnancy Usually 8 mm/Hg
• Resting Tone Decreased By
• Overdistension Of The Uterus
• Presence Of Incoordinate Uterine Action
• Pitocin Administration
• Resting Tone Increased By
• Anxiety
• Uterine Anomaly
• Uterine Fibroids
• Multiparity
• Debilitating Disease
• Narcotics
• Magnesium
• Tocolytic Agents
• Increase In Myometrial Tension Causes Inflow Of Maternal Blood To Intervillous Spaces To Essentially Cease At Intrauterine Pressures Of 50-60 Mm/Hg Thus Limiting Oxygen Transfer Warning Signs Of Impending Problems
• Contractions Longer Than 90 Seconds
• Relaxation Between Contractions Of Less Than 60 Seconds
• Resting Tone Above 200 Mm Hg
• Peak Pressure Of Contractions Above 90 Mm Hg (Except During Second Stage) These Four Signs Often Result Of
• Hyperstimulation Of Uterus Due To
• Oxytocin Stimulation
• Abuptio Placenta
• Pre-eclampsia
• Uterine Perforation
• Drugs
• Antihistamines
• Local Anesthetic Agents
• Prostaglandins E And F

  Electronic Fetal Monitoring Has Been Found To Be A Screening Test With Low Specificity, That Is, It Has A High False-positive Rate.

  Chalmers I, Enkin M, Kierse Mjnc (Eds) Effective Care In Pregnancy And Childbirth, Vol 2 Oxford: Oxford University Press, 1989

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