Ctg . Teach me everything. What it is, how to read one .teach me like a teacher. Take References from books like Williams Obstetrics and Gynecology, DC dutta. Teach me in super detail . Everything, all information

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I now have abundant, high-quality source material from Creasy & Resnik's Maternal-Fetal Medicine. Let me now compose the complete, comprehensive CTG teaching lesson.

📋 CARDIOTOCOGRAPHY (CTG) - A Complete Teaching Guide

Sources: Creasy & Resnik's Maternal-Fetal Medicine (Principles and Practice), Williams Obstetrics, DC Dutta's Textbook of Obstetrics

PART 1: WHAT IS A CTG?

Cardiotocography (CTG) is the simultaneous, continuous electronic recording of two things:

The Fetal Heart Rate (FHR) - the top channel
Uterine contractions (tonus/tocometry) - the bottom channel

The word comes from: Cardio (heart) + toco (labour/uterus) + graphy (writing/recording).

The machine that produces it is called an Electronic Fetal Monitor (EFM).

The paper strip it produces is called a CTG trace or cardiotocograph.

Why do we do it?

The fetal heart rate is tightly coupled to the fetal neurological and cardiovascular system. Changes in oxygenation, acid-base status, and autonomic nerve activity all reflect on the fetal heart. As Creasy & Resnik state: "FHR monitoring relies on the unique coupling of fetal neurologic status to cardiovascular reflex responses... it has become part of fetal monitoring of labor and delivery."

In short: the CTG is a window into the fetal brain and cardiovascular system. A well-oxygenated fetus has a specific pattern. A hypoxic fetus shows warning signs. A compromised fetus shows alarming patterns.

PART 2: THE PHYSIOLOGY BEHIND CTG

To read a CTG intelligently, you must understand the physiology first.

The Fetal Autonomic Nervous System

The FHR is controlled by two opposing systems:

Sympathetic nervous system - speeds the heart up
Parasympathetic (vagus) nerve - slows the heart down

In a healthy fetus, there is constant interplay between these two systems. This is why the FHR is never a flat line - it wiggles up and down constantly. This wiggling is called variability and it is the most important sign of fetal wellbeing.

Oxygen and the Fetal Brain

The fetus gets its oxygen from the mother via the placenta. The pathway is:

Uterine artery → Intervillous space → Placenta → Umbilical vein → Fetal circulation

During a uterine contraction, uterine blood flow temporarily decreases. A healthy fetus has enough reserve oxygen to withstand this. A compromised fetus cannot.

When fetal PO₂ falls:

Peripheral chemoreceptors in the fetus detect hypoxaemia
A vagal discharge is triggered
This causes a transient slowing of the heart (deceleration)
The brain also responds by reducing its oxygen consumption
Variability decreases as brainstem oxygenation falls

This sequence is the physiological basis of all abnormal CTG patterns.

The "Fetal Reserve" Concept

Think of it as a tank of oxygen. A healthy term fetus has a large reserve. A growth-restricted fetus, or one in a mother with preeclampsia, has a small reserve. Each contraction dips into that reserve. When the reserve runs out, the fetus decompensates.

PART 3: HOW THE MACHINE WORKS

The CTG machine has two transducers:

Transducer 1: For Fetal Heart Rate

There are two methods:

A. External (Doppler ultrasound transducer / cardiotachometer)

Placed on the maternal abdomen over the fetal back/chest
Emits a high-frequency ultrasound signal (~2.5 MHz)
Detects movement of cardiac valves or ventricular walls
Measures the interval between beats (in milliseconds), divides 60 by that interval to give rate in beats per minute
Uses autocorrelation technology to improve accuracy
Advantage: non-invasive, easy to apply
Disadvantage: can lose signal with maternal movements, obesity, or poor fetal positioning

B. Internal (Fetal Scalp Electrode / FSE)

A small spiral stainless steel wire screwed into the fetal scalp
Measures the R-wave of the fetal ECG directly
Gives true beat-to-beat variability - the most accurate method
Requires ruptured membranes and cervical dilation
Indication: when external monitoring is inadequate (e.g., maternal obesity)

Transducer 2: For Uterine Contractions (Tocometry)

A. External (Tocodynamometer / TOCO)

Placed on the fundus of the uterus
A pressure-sensitive button detects the hardening of the uterus during contractions
Shows the timing and frequency of contractions but NOT the actual intrauterine pressure
Cannot measure contraction strength accurately

B. Internal (Intrauterine Pressure Catheter / IUPC)

A soft plastic transducer-tipped catheter placed transcervically into the amniotic cavity
Measures actual intrauterine pressure in mmHg
Baseline uterine tone: ~8-12 mmHg
During contractions: typically 50-80 mmHg
Requires ruptured membranes
Useful when assessing adequacy of contractions (e.g., in failed induction)

The Paper

The CTG paper moves at a standard speed of 1 cm/min (UK) or 3 cm/min (USA). This is important because patterns look different at different speeds. Most UK hospitals use 1 cm/min. At 1 cm/min, each large square = 1 minute. Know your local paper speed before interpreting.

PART 4: THE CTG TRACE - ANATOMY OF THE STRIP

┌─────────────────────────────────────────────────────┐
│  FHR channel (top)    y-axis: 50-210 bpm            │
│  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  │
│  (wavy line representing fetal heart rate)          │
│                                                     │
│  Uterine activity (bottom)  y-axis: 0-100 mmHg      │
│  ___/\___/\___/\___  (mountains = contractions)     │
└─────────────────────────────────────────────────────┘

The top channel runs from 50 to 210 beats per minute (bpm). Normal range is around 110-160 bpm.

The bottom channel shows uterine contractions as gentle mounds (mountains).

PART 5: THE FIVE FEATURES TO ASSESS ON EVERY CTG

This is the systematic approach. Every time you look at a CTG, assess these five features in order. The mnemonic is DR C BRAVADO or simply remember: BRAVADO

Feature	What you measure
Baseline rate	The average FHR over 10 minutes
Rhythm / Regularity	Is it regular?
Accelerations	Are there accelerations?
Variability	How much does the FHR wiggle?
Absent features	Any decelerations?
Decelerations	Type and timing
Overall assessment	Category I / II / III

Let's go through each one in great detail.

FEATURE 1: BASELINE FETAL HEART RATE

Definition

The baseline FHR is the mean FHR rounded to the nearest 5 bpm during a 10-minute segment, excluding accelerations, decelerations, and periods of marked variability.

The 10-minute window must contain at least 2 minutes of interpretable baseline (not necessarily contiguous).

Normal Range

110-160 bpm (NICHD/ACOG/FIGO definitions)

Some texts give 120-160 bpm as the older range. The current accepted normal is 110-160 bpm.

Tachycardia

Defined as a baseline FHR >160 bpm persisting for at least 10 minutes.

Causes of fetal tachycardia:

Category	Causes
Maternal	Fever, infection (chorioamnionitis), thyrotoxicosis, anaemia, anxiety
Drug-induced	Beta-agonists (ritodrine, salbutamol), cocaine, methamphetamine, atropine
Fetal	Hypoxia (early warning sign), infection, anaemia, fetal arrhythmia
Physiological	Prematurity (baseline naturally higher), fetal activity

Key teaching point from Creasy & Resnik: "Although fetal tachycardia is potentially associated with fetal hypoxia, particularly when it is accompanied by decelerations of the FHR, the more common association is with maternal fever or fetal infection such as chorioamnionitis."

Do not confuse simple tachycardia with fetal tachyarrhythmia - if the FHR exceeds 240 bpm, that is a true arrhythmia (e.g., supraventricular tachycardia) and needs urgent evaluation.

Bradycardia

Defined as a baseline FHR <110 bpm persisting for at least 10 minutes.

Causes:

Category	Causes
Normal variant	Some fetuses simply run at 105-110 bpm
Cardiac	Congenital heart block (e.g., in maternal SLE/anti-Ro antibodies)
Drug-induced	Beta-blockers (e.g., propranolol, labetalol), anaesthetic agents
Hypoxic	Prolonged, severe hypoxia leading to vagal over-activity
Vasovagal	Maternal vasovagal episode, rapid epidural, aortocaval compression

Key distinction: A prolonged deceleration that establishes a new, lower rate can look like bradycardia. A true baseline bradycardia is when the low rate is the established baseline BETWEEN decelerations.

FEATURE 2: BASELINE VARIABILITY

This is arguably the most important feature on a CTG.

Definition

Baseline variability refers to the fluctuations in the baseline FHR of 2 cycles per minute or greater. It is measured as the amplitude of the fluctuations (the difference between the highest and lowest points within a 1-minute window, excluding accelerations and decelerations).

Types of Variability (NICHD Classification)

Classification	Amplitude	Clinical Meaning
Absent	Undetectable (<2 bpm)	Severely worrying
Minimal	>0 but ≤5 bpm	Worrying if persistent
Moderate (Normal)	6-25 bpm	Normal, reassuring
Marked	>25 bpm	Usually benign (saltatory pattern)

The golden rule: If variability is moderate (6-25 bpm), regardless of what other patterns are present, the fetal brain is adequately oxygenated and the fetus is NOT experiencing metabolic acidosis. This is the most protective sign on a CTG.

From Creasy & Resnik: "If the FHR variability is normal, regardless of what other FHR patterns may be present, the fetus is not experiencing cerebral tissue hypoxemia because the fetus can centralize the available oxygen and is physiologically compensated."

Physiological Basis of Variability

Variability reflects the integrity of the entire arc from:

Cerebral cortex
Midbrain
Vagus nerve
Cardiac conduction system

It is essentially proof that the fetal brain is alive, awake, and in control of the heart. Loss of variability = the brain is losing control = hypoxia/acidosis developing.

Non-Hypoxic Causes of Reduced Variability

Before calling a flat trace "hypoxic," always consider:

Fetal sleep cycle - fetuses sleep in 20-40 minute cycles; during quiet sleep, variability physiologically decreases (minimal). A sleep cycle never exceeds 40-60 minutes.
Narcotics/opioids - pethidine, morphine, fentanyl all suppress CNS and reduce variability (Fig. 33.3 in Creasy & Resnik shows a flat trace in a mother on magnesium sulfate and narcotics with normal scalp pH 7.28)
Magnesium sulfate - CNS depressant
Benzodiazepines (diazepam, lorazepam)
Prematurity - preterm fetuses naturally have lower variability
Anencephaly - no cortex, no variability
Complete heart block - defective cardiac conduction
Atropine/scopolamine - vagal blockade

Clinical rule: If variability is absent and the fetus has received pethidine in the last 2-4 hours, consider a prolonged monitoring period or fetal scalp pH before acting. If variability is absent with no pharmacological explanation AND there are late decelerations, act urgently.

Saltatory Pattern (Marked Variability >25 bpm)

Excessively large amplitude fluctuations. Usually seen transiently during cord compression. Significance uncertain but persistent saltatory pattern with decelerations is concerning.

Variable decelerations on a CTG trace showing the top FHR channel and bottom uterine activity channel

CTG showing variable decelerations with normal baseline variability between decelerations - Creasy & Resnik

FEATURE 3: ACCELERATIONS

Definition

A visually apparent, abrupt increase in FHR above baseline.

For ≥32 weeks gestation:

Peak ≥ 15 bpm above baseline
Duration ≥ 15 seconds but < 10 minutes

For < 32 weeks gestation:

Peak ≥ 10 bpm above baseline
Duration ≥ 10 seconds

If an acceleration lasts ≥10 minutes, it is classified as a baseline change, not an acceleration.

Significance

Accelerations are the most reliable sign of fetal wellbeing.

They reflect:

An intact fetal nervous system
Adequate oxygenation of the CNS
Fetal movement triggering autonomic activity

The Non-Stress Test (NST) is based entirely on accelerations. A reactive NST = at least 2 accelerations in 20-30 minutes. This is the definition used in the Biophysical Profile.

From Creasy & Resnik: "The classic criteria for a reactive NST are at least two FHR accelerations lasting at least 15 seconds and rising at least 15 beats/min above the established baseline heart rate. Most term fetuses have many of these accelerations in each 20-30 minute period of active sleep."

Absence of Accelerations

When there are NO accelerations on a CTG in labour:

Does NOT by itself indicate fetal compromise
However, absence of accelerations alongside other features (reduced variability, decelerations) increases concern
Requires closer monitoring

Overshoot / Shoulder

A brief acceleration immediately preceding or following a deceleration is called an "overshoot" if it follows a variable deceleration. This is a non-reassuring sign and may indicate hypoxic sympathetic stimulation.

FEATURE 4: DECELERATIONS

A deceleration is a visually apparent decrease in FHR below the baseline. There are four main types. Getting these right is the core clinical skill of CTG interpretation.

Key parameters for any deceleration:

Onset - abrupt (within <30 seconds) vs. gradual (>30 seconds)?
Timing - when does the nadir occur relative to the peak of the contraction?
Duration - seconds
Depth - nadir below baseline (bpm)
Variability during/between - does the FHR recover with good variability?
Uniformity - do they all look the same or are they different each time?

TYPE 1: EARLY DECELERATIONS

Shape: Uniform, smooth, symmetrical U-shape, mirror image of the contraction Onset: Gradual (>30 sec to nadir) Timing: Begins WITH the start of the contraction, nadir at the PEAK of contraction, returns to baseline as contraction ends - perfectly in phase Depth: Usually mild, rarely below 100 bpm Cause: Fetal head compression against the cervix → vagal stimulation → transient heart rate slowing (Baroreflex)

Clinical significance: BENIGN. Not associated with fetal hypoxia or acidosis. Seen most commonly in active labour with cervical dilation.

Contraction:    ___/\___
FHR change:     ___\/___   (mirror image = simultaneously occurring)

TYPE 2: LATE DECELERATIONS

This is the most important deceleration type to recognise.

Shape: Uniform, smooth, symmetrical U-shape Onset: Gradual (>30 sec to nadir) Timing: Begins AFTER the peak of the contraction, nadir is DELAYED after peak contraction, returns to baseline after the contraction has completely ended Depth: Can be shallow (even 10-20 bpm below baseline) or deep Cause: Uteroplacental insufficiency

Contraction:    ___/\___
FHR change:         ___\/___   (shifted to the right - delayed)

The Physiology of Late Decelerations (in detail from Creasy & Resnik):

There are TWO types of late decelerations:

1. Reflex late decelerations (with GOOD variability)

Mechanism: Acute drop in uterine blood flow during contraction → placental hypoperfusion → fetal PO₂ drops → fetal chemoreceptors detect hypoxaemia → vagal discharge → heart rate slows
Timing is late because of the circulation time from placenta to chemoreceptors
The fetal brain and myocardium still have adequate oxygen (just barely)
Variability is maintained = brain is still in control = physiologically compensated
Seen in: acute hypotension, epidural, aortocaval compression, acute blood loss

2. Non-reflex late decelerations (with ABSENT variability)

Mechanism: The deoxygenated blood from placenta is so profoundly hypoxic that it directly depresses the myocardium + increases vagal activity
The brain has run out of oxygen too - it can no longer maintain variability
Variability is absent = fetal decompensation = cerebral and myocardial hypoxia
Seen in: severe preeclampsia, IUGR, prolonged hypoxia after recurrent late decelerations

From Creasy & Resnik: "Nonreflex late decelerations occur without FHR variability, signifying fetal decompensation - inadequate cerebral and myocardial oxygenation."

Clinical significance: ANY late deceleration is abnormal and requires assessment. Persistent late decelerations, especially with reduced variability, are associated with fetal acidosis and require urgent intervention.

Important: Even shallow late decelerations (only 10-15 bpm) are significant. Depth does not determine pathology - timing does.

TYPE 3: VARIABLE DECELERATIONS

Shape: Variable - each deceleration looks different. Sharp, abrupt, often V-shaped or W-shaped Onset: Abrupt (< 30 seconds from onset to nadir) Timing: Variable relationship to contractions - may come before, during, or after Depth: Variable, can be very deep (down to 60-70 bpm) Cause: Umbilical cord compression

Typical variable deceleration: 
FHR: ____/|\_/|____
         Shoulders = brief accelerations before/after deceleration

The Shoulders: Variable decelerations often have brief accelerations immediately before and after them. These "shoulders" are a reassuring sign that the autonomic nervous system is intact.

Physiology:

Cord compression → increased fetal blood pressure → baroreceptor reflex → vagal activity → heart rate drops
The abrupt onset reflects the sudden nature of cord occlusion
Recovery is usually quick once the cord is released

Simple vs. Complicated Variable Decelerations:

Feature	Simple (Reassuring)	Complicated (Non-reassuring)
Duration	<60 seconds	>60 seconds
Depth	<60 bpm nadir	<60 bpm nadir (i.e. drops very deep)
Shoulders	Present	Absent
Baseline variability	Normal between decelerations	Reduced
Recovery	Complete, returns to baseline	Slow, incomplete
Post-deceleration overshoot	Absent	Present (prolonged)

Variable decelerations in 2nd stage: Very common. The fetal head is being compressed and the cord is under intermittent pressure. Brief variable decelerations in 2nd stage with maintained variability are generally acceptable.

TYPE 4: PROLONGED DECELERATIONS

Definition: A fall in FHR of ≥15 bpm lasting ≥2 minutes but <10 minutes

If it lasts ≥10 minutes, it is a baseline change (bradycardia).

Causes:

Cord prolapse
Placental abruption
Maternal hypotension (e.g., post-epidural top-up)
Uterine hyperstimulation (tachysystole)
Maternal Valsalva / second-stage pushing
Vaginal examination stimulating cervical receptors
Maternal seizure

Clinical significance: Always take a prolonged deceleration seriously. If it lasts >3 minutes with no obvious remediable cause, urgent assessment is needed. If it persists >9 minutes, prepare for immediate delivery.

From Creasy & Resnik: "Among 951 patients who had a terminal deceleration in the study, 98% did not have a neonate with a pH less than 7.10. However, increasing terminal deceleration duration was associated with decreasing umbilical artery pH and increased risk of acidemia."

SINUSOIDAL PATTERN

This is a rare but important pattern.

Definition: A smooth, sine wave-like undulating pattern with a fixed periodicity of 3-5 cycles/minute and an amplitude of 5-15 bpm lasting ≥20 minutes. There are NO accelerations and NO beat-to-beat variability.

Causes:

Severe fetal anaemia (Rh isoimmunization, fetomaternal haemorrhage, parvovirus B19)
Fetal hypoxia
Drug-induced pseudo-sinusoidal: pethidine, butorphanol (this reverses within 30 min)

Key distinction: A TRUE sinusoidal pattern = fetal anaemia until proven otherwise. Requires URGENT evaluation (Kleihauer test, middle cerebral artery Doppler for peak systolic velocity).

PART 6: THE NICHD THREE-TIER CLASSIFICATION SYSTEM (2008)

This is the internationally adopted system by the National Institute of Child Health and Human Development, endorsed by ACOG, for classifying CTG tracings.

CATEGORY I - NORMAL (Reassuring)

ALL of the following:

Baseline FHR: 110-160 bpm
Baseline FHR variability: moderate (6-25 bpm)
Accelerations: present or absent
Late or variable decelerations: absent
Early decelerations: present or absent

Meaning: Strongly predictive of normal fetal acid-base status. No action required beyond routine monitoring.

CATEGORY II - INDETERMINATE (Requires Evaluation)

All tracings that are NOT Category I or Category III fall here. Examples include:

Baseline tachycardia
Baseline bradycardia (not Category III)
Minimal variability (without decelerations)
Absent variability (without recurrent decelerations)
Marked (saltatory) variability
Absence of induced accelerations after fetal scalp stimulation
Recurrent variable decelerations with minimal or moderate variability
Prolonged deceleration >2 minutes but <10 minutes
Recurrent late decelerations with moderate variability
Variable decelerations with other features (slow return, "overshoots," shoulders)

Meaning: Insufficient evidence to classify as normal or abnormal. Requires continued surveillance, evaluation for remediable causes, and possible escalation.

CATEGORY III - ABNORMAL (Requires Prompt Action)

Either of the following:

Sinusoidal pattern, OR
Recurrent late decelerations with absent baseline variability, OR
Recurrent variable decelerations with absent baseline variability, OR
Bradycardia with absent baseline variability

Meaning: Associated with abnormal fetal acid-base status. Requires PROMPT evaluation and delivery if the pattern cannot be corrected.

THE UK SYSTEM: NICE GUIDELINES (for comparison)

The UK NICE guidelines classify CTG features as:

Feature	Reassuring	Non-reassuring	Abnormal
Baseline	110-160 bpm	100-109 bpm or 161-180 bpm	<100 or >180 bpm; sinusoidal
Variability	≥5 bpm	<5 bpm for 30-90 min	<5 bpm for >90 min
Decelerations	None or early	Variable for <90 min OR late for <30 min	Atypical variable or late for >30 min
Accelerations	Present	Absent	-

Then the overall CTG is classified as:

Normal - all four features reassuring
Suspicious - one non-reassuring feature
Pathological - two or more non-reassuring OR one or more abnormal features

PART 7: DECELERATIONS COMPARED - QUICK REFERENCE TABLE

Feature	Early	Late	Variable	Prolonged
Onset	Gradual	Gradual	Abrupt	Either
Timing vs contraction	Simultaneous (mirrors it)	AFTER contraction	Variable/random	>2 min after onset
Shape	Uniform, U	Uniform, U	V or W, irregular	Deep, prolonged
Duration	= contraction	Outlasts contraction	<2 min usually	2-10 min
Cause	Head compression	Uteroplacental insufficiency	Cord compression	Multiple
Significance	Benign	Pathological	Depends on features	Serious
Variability	Normal	Normal (reflex) or absent (non-reflex)	Normal between	Depends

PART 8: FETAL ACID-BASE STATUS - WHAT THE CTG PREDICTS

Understanding the acid-base connection is what makes CTG clinically meaningful.

Fetal Acidaemia Thresholds (Creasy & Resnik)

Umbilical Artery pH	Clinical Significance
>7.20	Normal
7.10-7.20	Mild acidaemia, usually no adverse outcome
7.00-7.10	Significant acidaemia, increasing risk of neonatal complications
<7.00	Pathological acidaemia - associated with 8% neonatal death, 9.2% seizures

Note: Mean umbilical artery pH at birth is ~7.27-7.28 (SD ~0.07).

The critical pH threshold for meaningful morbidity is 7.00. Below this, rates of seizures and neonatal death rise significantly (Goldaber et al., 1991).

Base deficit >12 mmol/L = significant metabolic acidosis even if pH is borderline.

Types of Fetal Acidaemia

Type	pH	PCO₂	HCO₃⁻	Cause
Respiratory	↓	↑↑	Normal	Acute cord compression, short duration
Metabolic	↓	Normal	↓↓	Prolonged hypoxia, anaerobic metabolism
Mixed	↓	↑	↓	Both mechanisms together

Respiratory acidosis is usually acute and reversible. It occurs with sudden cord compression or uterine hyperstimulation.

Metabolic acidosis is the dangerous type. It builds up slowly with prolonged hypoxia. The pH may fall to 7.00 or below, and base deficit rises. This is associated with hypoxic-ischaemic encephalopathy (HIE).

PART 9: CLINICAL MANAGEMENT - WHAT TO DO

For Category I (Normal)

Continue routine monitoring
Document regularly (every 30-60 min)

For Category II (Indeterminate)

Step 1 - Correct remediable causes (Intrauterine Resuscitation):

Problem	Action
Maternal position (aortocaval compression)	Left lateral tilt / full left lateral position
Maternal hypotension (post-epidural)	IV fluid bolus, ephedrine/phenylephrine if needed
Uterine hyperstimulation	Stop oxytocin, consider tocolysis (terbutaline 0.25 mg SC)
Cord prolapse	Emergency delivery
Maternal hypoxia	Give supplemental oxygen (though recent evidence shows limited benefit on fetal pH)

Step 2 - Fetal Scalp Stimulation (FSS) / Allis clamp test:

Apply pressure or Allis clamp to fetal scalp through the dilated cervix
A resulting acceleration = pH >7.20 (NPV ~99%)
No acceleration = indeterminate, may need further assessment

Step 3 - Fetal Scalp Blood Sampling (FBS) - where available:

Scalp pH >7.25 = normal (repeat in 1 hour if CTG still abnormal)
Scalp pH 7.20-7.25 = borderline (repeat in 30 min)
Scalp pH <7.20 = acidaemia → expedite delivery

From Creasy & Resnik: "Fetal scalp blood sampling is no longer an option in most hospitals providing obstetric care" (due to quality assurance issues and procedural challenges).

For Category III (Abnormal)

Immediate actions (all simultaneously):

Left lateral position
Stop oxytocin
IV fluid bolus
Supplemental oxygen (face mask)
Call senior obstetrician
If no improvement in 10-15 min → expedite delivery
- Category 1 (crash) caesarean if immediate danger
- Or assisted vaginal delivery if feasible and rapid

PART 10: SPECIAL SITUATIONS

Prematurity

Preterm fetuses (<32 weeks) have higher baseline rates and lower variability as a baseline feature
Accelerations are smaller (10 bpm, 10 seconds qualifies as reactive)
Late decelerations still carry the same significance
Interpretation must be modified for gestational age

Multiple Pregnancy

Two separate CTG traces needed for twins
Difficult to distinguish the two in external monitoring
Use FSE on presenting twin if possible
Variable decelerations are more common in monochorionic twins due to cord entanglement

Second Stage of Labour

Variable decelerations are very common due to cord compression by the descending head
The important questions are: Is variability maintained? Are decelerations recovering completely? Is the baseline stable?
Brief (< 60 seconds), uncomplicated variable decelerations with maintained variability in the second stage are acceptable
Prolonged variable decelerations or those with loss of variability require action

Post-dates Pregnancy

Placental reserve declines after 40-42 weeks
Late decelerations are more significant
Oligohydramnios (reduced liquor) increases cord compression risk
CTG alone is insufficient for post-dates surveillance - combine with AFI/BPP

PART 11: SYSTEMATIC APPROACH TO READING A CTG - STEP BY STEP

Every time you pick up a CTG trace, use this approach:

Step 1: Confirm patient details, gestational age, date/time, paper speed

Step 2: Look at the overall picture - do you see a reassuring or worrying trace at a glance?

Step 3: Assess baseline rate - is it 110-160? Is it tachycardic or bradycardic?

Step 4: Assess variability - 6-25 bpm (moderate)? Minimal? Absent?

Step 5: Look for accelerations - present? How many?

Step 6: Identify decelerations - what type? Early, late, variable, prolonged?

For each deceleration: when does it start relative to contraction? When does it reach nadir? How deep? How long? What is variability doing?

Step 7: Look at uterine activity - how frequent are contractions? Any hyperstimulation (>5 in 10 min)?

Step 8: Classify - Category I, II, or III?

Step 9: Document your interpretation with timestamp and action taken

PART 12: LIMITATIONS OF CTG

CTG is NOT a perfect test. This is important to understand.

From Creasy & Resnik: "Several well-designed randomized clinical studies from different clinical centers involving almost 40,000 women in labor have demonstrated that intrapartum EFM does not result in any measurable improvement in outcomes compared with intermittent auscultation."

Key limitations:

High false positive rate - many abnormal CTGs are in non-acidotic fetuses
Poor interobserver agreement - two clinicians may classify the same trace differently
The only proven benefit is reduction in neonatal seizures (not long-term neurological outcomes)
The rate of caesarean section increased dramatically after CTG was introduced
EFM does NOT significantly reduce perinatal death, cerebral palsy, or HIE
Only 0.19% of children with abnormal FHR findings developed cerebral palsy (Creasy & Resnik)

Why still use CTG then?

It remains the best available tool for continuous intrapartum surveillance
It has high sensitivity (few missed hypoxic events)
Combined with fetal scalp stimulation, it has good NPV
Practical and non-invasive
Alternative (intermittent auscultation) is labour-intensive and not feasible in high-risk cases

PART 13: CTG IN ANTENATAL PERIOD - THE NON-STRESS TEST (NST)

CTG is not just for labour. In the antenatal period, it is used as the NST.

Reactive NST

2 accelerations in 20-30 min (each ≥15 bpm, ≥15 sec at term; or ≥10 bpm, ≥10 sec before 32 weeks)
Falsely reassuring (false negative) rate: ~1.9 per 1000 fetuses per week (excellent)

Non-reactive NST

Does not meet criteria after 40 minutes
Proceed to biophysical profile (BPP) or contraction stress test (CST)
About 10-12% of third trimester fetuses are non-reactive at 30 min (usually due to sleep cycle)

Contraction Stress Test (CST)

Nipple stimulation or oxytocin infusion to produce at least 3 contractions in 10 minutes
Negative (normal): No late decelerations
Positive (abnormal): Late decelerations with ≥50% of contractions
Suspicious: Intermittent late decelerations
A positive CST indicates uteroplacental insufficiency

SUMMARY MEMORY AID

NORMAL CTG (Category I):
- Baseline: 110-160 bpm
- Variability: 6-25 bpm (moderate)
- Accelerations: present
- Decelerations: none (or only early)
- "All is well"

WARNING SIGNS (look for):
- Rising baseline (early hypoxia → tachycardia)
- Falling variability (brain struggling)
- Loss of accelerations
- Late decelerations (uteroplacental failure)
- Deep/prolonged variable decelerations
- Sinusoidal pattern (anaemia)

THE SINGLE MOST IMPORTANT FEATURE:
→ VARIABILITY. Good variability protects everything else.
→ Even with late decelerations: if variability is good = reflex = brain compensated.
→ Absent variability + ANY decelerations = decompensated = emergency.

References

Creasy RK, Resnik R et al. Creasy & Resnik's Maternal-Fetal Medicine: Principles and Practice, 9th Edition. Elsevier. Chapters 32 & 33: Fetal Heart Rate Monitoring, Acid-Base Assessment.
Williams Obstetrics (Cunningham et al.) - Electronic Fetal Monitoring chapter
DC Dutta. Textbook of Obstetrics, 10th Edition - Fetal Surveillance chapter
NICHD Workshop Report (2008) - Three-tier FHR classification system (ACOG)
NICE Guideline CG190 - Intrapartum Care for Healthy Women and Babies (UK)
Goldaber KG et al. Pathologic fetal acidemia. Obstet Gynecol. 1991;78:1103.

That is the complete CTG teaching guide. If you want, I can drill down deeper into any specific section - for example, practice trace interpretation, the biophysical profile scoring system, the STAN (fetal ECG ST analysis) adjunct, or management algorithms for specific clinical scenarios. Just say the word.

Create a detailed CTG practice cases workbook with 10 real traces to interpret

Create a detailed CTG practice cases workbook with 10 real traces to interpret. Give answers and how u arrived at the result. All explanations.

Finding Sources

Reading File

Finding Sources

Reading File

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Reading File

Running Command

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