The document summarizes the key aspects of non-stress tests (NSTs) used to monitor fetal heart rate (FHR) patterns during pregnancy. It describes how NSTs use Doppler ultrasound to externally monitor FHR. It defines normal and abnormal FHR patterns including baseline rate, variability, accelerations, decelerations, and other periodic changes. It discusses how different FHR patterns may indicate issues like cord compression, fetal distress, or placental insufficiency. It also outlines guidelines for normal NST results and follow-up based on findings.

1. Non Stress Test
N S T

2. • External (indirect) electronic monitoring of FHR
• Based on ultrasound Doppler principle
• Unit consists of
• Transducer – emits ultrasound
• Sensor – detects shift in frequency of reflected sound
• Require coupling gel – air conducts ultrasound waves poorly
• Correct positioning – can differentiate fetal cardiac motion from
maternal arterial pulsations
• Reflected ultra sound signals are analyzed through a micro
processor, that compares incoming signals with most recent
previous signal – autocorrelation

3. FHR Patterns
• Mean FHR with increments of 5 bpm in 10mins excluding
- Periodic/ episodic changes
- Marked FHR variability
- Baseline segment differ by more than 25 bpm
• Minimum 2 min in 10 min segment
• Normal FHR – 110 to160 bpm
• Tachycardia > 160 bpm
• Bradycardia < 110 bpm
Baseline
• Baseline fluctuations with irregular amplitude and
frequency
• Amplitude of peak to trough in bpm
• Absent – amplitude range is undetectable
• Minimal – detectable but less than equal to 5 bpm
• Moderate (Normal) – 6 to 25 bpm
• Marked – more than 25 bpm
Baseline Variability

5. • Abrupt increase in FHR (Onset to peak in less than 30
sec)
• At or beyond 32 wk – peak of 15 bpm or more lasting
for 15 sec or more but less than 2 mins from onset to
return
• Before 32 weeks – peak of 10 bpm or more lasting for
10 sec or more but less than 2 mins from onset to
return
• Prolonged acceleration – lasts 2 mins or more but less
than 10 mins
• 10 mins or longer – baseline change
Acceleration
• Symmetrical gradual decrease (>= 30 sec) and return of FHR
associated with uterine contraction
• Lowest point of deceleration coincide with peak of contraction
Early Deceleration

6. • Lowest point of deceleration occur after the peak of
contraction
• Onset, lowest point and recovery of deceleration occur
after the beginning, peak & ending of the contraction
respectively
Late Deceleration
• Abrupt fall in FHR
• From Onset to the lowest point of FHR within 30 sec
• Decrease in FHR is 15 bpm or greater , lasting 15 sec or
greater & less than 2 mins in duration
• Onset, depth and duration vary with successive uterine
contractions
Variable
Deceleration

7. • Decrease in FHR below baseline i.e. 15 bpm or more and
more than 2 mins duration
• Deceleration last 10 mins or longer – baseline change
Prolonged
Deceleration
• Apparent, smooth, sine wave pattern in FHR baseline
with a cyclic frequency of 3- 5 per mins which persists
for 20 mins or more
Sinusoidal pattern
NICHD – propose standardized definitions for interpretation of FHR pattern during labor.
- modified in 2008  adopted by ACOG
30 bpm per vertical cm (Range – 30 to 240bpm) and 3 cm per min chart recorder paper speed

10. Baseline Fetal Heart Activity
Rate
• With an increase in fetal maturation – FHR decreases, continues post natally
• Decline an average of 24 bpm b/w 16 wk to term
• Due maturation of parasympathetic (vagal) heart control
• Avg FHR – result of tonic balance b/w symp and parasymp influences on
pacemaker cells
– under the control of arterial chemoreceptors[ prolonged hypoxia with
rising blood lactate level & severe metabolic acidemia  fall FHR

11. Bradycardia
• T3 – normal FHR 120 to 160 bpm
• 100 to 119 bpm in the absence of other changes – not represent
fetal compromise
• 80 to 120 bpm with good variability – reassuring
• < 80 bpm – non reassuring
• Causes
• Congenital heart block
• Serious fetal compromise – placental abruption/hypoxia/sepsis
• Maternal hypoglycemia /hypothermia
• Drugs to mother-pethidine,antihypertensive,mgso4
• Severe pyelonephritis

12. Tachycardia
Causes
 Maternal fever
 Fetal compromise-hypoxia,infection
 Cardiac arrhythmia
 Drugs to mother-
sympathomimetic[isoxsuprine,ritodrine],parasymp
inhibiting[atropine]
 Maternal hypotension
 Anemia-maternal/fetal

13. Beat to Beat variability
• Important index of cardio vascular function
• Regulated by ANS
• Short term variability – instantaneous change from 1 beat to the next
– measure of time interval b/w cardiac systoles
– most reliably determined by scalp electrode
• Long term variability – oscillatory changes during 1min & result in the
waviness of the baseline
– normal frequency 3 to 5 cycles per min

15. • Increased variability – fetal breathing and body movements
– advancing gestation
• Up to 30 wks - similar baseline characteristics in fetal rest and activity
• After 30 wks – fetal inactivity  diminished variability
– fetal activity  enhance
• Baseline FHR becomes less variable as rate rises
• Decreased variability – causes
• Analgesics
• CNS depressant drugs (transient variation) – Narcotics, barbiturates,
phenothiazine's, tranquilizers, general anaesthetics
• Corticosteroids
• MgSO4 – without adverse neonatal effects
• Severe maternal acidemia – DKA  Depression of fetal brainstem or the heart itself
creates loss of variability

16. • Diminished BBV with fetal compromise – due to acidemia (not hypoxia)
• Absent variability – within the normal baseline rate range and without
deceleration  previous fetal insult resulted in neurological damage
Sinusoidal heart rate
Seen in
• Fetal intracranial hemorrhage
• Severe fetal asphyxia
• Severe fetal anemia – anti D alloimmunization, feto maternal
hemorrhage, TTTS, fetal parvo viral inf, vasaprevia with bleeding
• Narcotics – sine frequency of 6 cycles per min
• Chorioamnionitis
• Fetal distress
• Umbilical cord occlusion

17. Features of sinusoidal pattern
• Stable baseline FHR of 120 to 160 bpm with regular oscillations
• Amplitude of 5 to 15 bpm
• Long term variability frequency of 2 to 5 cycles per min
• Fixed or flat short term variability
• Oscillations of sinusoidal waveform above or below a baseline
• Absent acceleration
Intrapartum sine wave like baseline variation with periods of
acceleration – pseudo sinusoidal
• Mild – epidural
• Intermediate – transient episodes of fetal hypoxia caused by
umbilical cord compression

18. Periodic FHR changes
Accelerations
• Represent intact neurohormonal cardio vascular control mechanisms linked to fetal
behavioral states
• Always reassuring – no acidemia
• Seen in
• Fetal movement
• Stimulation by uterine contraction
• Umbilical cord occlusion
• Fetal stimulation during pelvic examination
• Scalp blood sampling
• Acoustic stimulation

19. Early Deceleration
• Head compression  Dural stimulation  vagal nerve activation  early
deceleration
• Degree of deceleration is proportional to contraction strength
• Rarely falls below 100 to 110 bpm or 20 to 30 bpm below baseline
• Common during active labor
• Not associated with fetal hypoxia or acidemia
Late Deceleration
• Utero placental insufficiency
• Magnitude is not more than 30 to 40 bpm below baseline (typically 10 to 20 bpm)
• Seen in
• Maternal Hypotension – epidural
• Uterine hyper activity – oxytocin stimulation
• Chronic placental dysfunction – maternal disease (HTN, DM, collagen vascular disorders)
• Placental abruption – acute late deceleration

20. Variable Deceleration
• Cord compression
• 2 types
a) Type A – seen in complete occlusion
b) Type B – due to differing degrees of partial occlusion
– Acceleration before and after
– Vein occlusion  reduce fetal blood return  trigger baroreceptor mediated
acceleration
– With increase in intrauterine pressure  complete cord occlusion  obstruction of
umbilical artery flow  fetal systemic HTN  baroreceptor mediated deceleration
– vagal response due to chemo/baro receptor activity
• Recurrent variable deceleration with minimal to moderate BBV are indeterminate whereas
those with absent variability are abnormal

22. Other FHR patterns
(associated with umbilical cord compression)
• Saltatory baseline HR – rapidly recurring couplets of acceleration & deceleration
– seen in post term pregnancies
• Lambda – acceleration followed by a variable deceleration with no acceleration at the end
of deceleration
– seen in early labor
– Result from mild cord compression or stretch
• Overshoot - variable deceleration followed by acceleration

23. Prolonged deceleration
Causes
• Cervical examination
• Uterine Hyperactivity
• Cord Entanglement
• Maternal Supine Hypotension
• Epidural / Spinal / Paracervical analgesia
• Maternal hypo perfusion / Hypoxia from any cause
• Placental abruption
• Umbilical cord knots / prolapse
• Maternal Seizure
• Application of fetal scalp electrode
• Impending birth or maternal valsalva maneuver
• Placenta is effective in resuscitating the fetus if the original insult does not recur
immediately
• Fetus may die during prolonged decelerations

24. Normal NST
• More than or equal to 2 accelerations peaking at 15 bpm or more
above baseline, each lasting 15 secs or more within 20 mins of test
• Acceleration with or without fetal movements – 40 mins tracing
(fetal sleep cycle)
• Long duration NST – Not move up to 75 mins  reactive within 80
mins/ non reactive for 120 mins (very ill)
• Absence of acceleration in 80 min recording – uteroplacental
pathology
• IUGR
• Oligohydramnios
• Fetal acidemia
• Meconium
• Placental infarction
• Interval b/w testing – 7 days
• Twice weekly – post term pregnancy , multi fetal gestation , pregest DM, IUGR,
GHTN
• Daily – severe PE
• Repetitive deceleration – 3 in 20 mins OR accompany more than 50%
of contractions in 20 mins  Fetal distress

25. • False normal NST – fetal death within 7 days (post term pregnancy)
• Mean interval b/w testing and death - 4 days (1 to 7 days)
• Causes of fetal death
• Intrauterine infection
• Abnormal cord position
• Malformation
• Placental abruption
FHR patterns during second stage of labor
• Decelerations are common due to both cord and fetal head compression
• If prolonged  still birth and neonatal death
• If total no. of decelerations < 70 bpm increased, persistent baseline brady /tachy –
decreased APGAR

26. 3 tier FHR interpretation system
Category 1 – normal
• Baseline rate – 110 to 160 bpm
• Baseline FHR variability – moderate
• Late or variable decelerations- absent
• Early decelerations – present / absent
• Accelerations – present / absent
Category 2 – Indeterminate
• Baseline rate
• Bradycardia not accompanied by absent baseline variability
• Tachycardia
• Baseline FHR variability
• Minimal baseline variability
• Absent variability not accompanied by recurrent decelerations
• Marked baseline variability

27. • Accelerations
• Absence of induced accelerations after fetal stimulation
• Periodic / Episodic decelerations
• Recurrent variable decelerations with minimal or moderate baseline variability
• Prolonged deceleration
• Recurrent late decelerations with moderate baseline variability
• Variable decelerations with other characteristics – slow return to baseline, overshoot,
shoulders
Category 3 – Abnormal
Include either
• Absent baseline FHR variability & any of the following
• Recurrent late decelerations
• Recurrent variable decelerations
• Bradycardia
• Sinusoidal pattern

28. Resuscitative measures for Category II or III Tracings
FHR abnormality Interventions
Recurrent late decelerations
Prolonged decelerations or Brady
Minimal/Absent FHR variability
Lateral decubitus positioning, administer
maternal oxygen, IV fluid bolus, reduce
uterine contraction frequency
Tachysystole with category II or III tracing Discontinue oxytocin or PG, give tocolytics –
MgSO4, Terbutaline
Recurrent variable decelerations
Prolonged decelerations or brady
Reposition mother, amnioinfusion, with cord
prolapse – manually elevate the presenting
part while preparing for immediate delivery

32. Thank You