Obstetrics

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