Ant-partum Fetal Evaluation
Professor Hassan Nasrat
By the end of this Lecture you should be able to :
-List the objectives of antepartum fetal surveillance
-Discusses the fetal response to hypoxia (patho-physiology of
fetal response to hypoxia): The compensation and decomposition
of the fetus to hypoxia.
-List the methods of fetal monitoring:
OFetal Movements count:
oElectronic Fetal Heart Monitoring (Non-Stress Test and
Contractions Stress test):
oBiophysical Profile (BPP):
oViboracustic Stimulation:
oDoppler Blood Flow:
-For Each method you should be able to describe :
The principle, technique and interpretation.
Objectives and indications of prenatal fetal
monitoring
Primary goal: To Prevent fetal Death
Secondary goal: Prevent neurologic injury
from prolonged exposure to intrauterine
hypoxia.
Indications For Fetal Surveillance
Indications For Fetal Surveillance
1.Patients at high risk of uteroplacental insufficiency e.g.:
 Prolonged pregnancy.
Hypertension
Diabetes
Previous stillbirth
Suspected FGR
Multiple pregnancy
Advanced maternal age
Antiphospholipid syndrome
2.When other tests suggest fetal compromise e.g.:
 Suspected FGR (on clinical examination)
Decreased fetal movements
Oligohydramnios
Neurological Maturation of Fetal function
and
Patho-physiology of fetal Hypoxia:
Neurological Maturation of
Fetal function
Maturation of the fetal neurological function
occurs in stages:
The Fetal Tone And Movements: (Between 7 -9
Weeks)
Fetal Heart Reactivity: The Parasympathetic then
the sympathetic system.
The Breathing Movements: Are Controlled By
The Breathing Center In Brain Stem. Breathing
Movements Start To Appear From Early Second
Trimester.
Pathophysiology of fetal
Hypoxia
General principles in Interpretation of Fetal
monitoring
Interpretation of any of the methods of fetal
monitoring should take in consideration some factors:
 gestational age,
maternal conditions
(E.g. administration of steroid for fetal
lung maturity is associated with reduced BPP for period up to 3
days),
Fetal condition (e.g. GR, anemia, arrhythmia).
more than one method should be used because of
the limited sensitivity of most of them.
Interpretation of Fetal monitoring
Depending on:
The Results Of The Tests.
Gestational Age.
And Overall Clinical Situation,
delivery may be warranted if the risks of
continuing the pregnancy outweigh the
benefits .
Methods of fetal surveillance during pregnancy
 Fetal Movements count:
 Electronic Fetal Heart Monitoring (NonStress Test and contractions stress test):
 Biophysical Profile (BPP):
 Viboracustic Stimulation:
 Doppler Blood Flow:
1) Maternal Assessment of Fetal Activity (Fetal
Movement Count Chart):
Advantage: low cost but also can be offered to almost all women
Principle:
Normal fetal movement is a sign of functional integrity of fetal
neuro-regulatory systems. In the presence of mild hypoxemia,
the fetus compensate by decreased frequency and strength of
movements. Hence decreased fetal movement is considered a
warning sign for further fetal evaluation.
The Technique: A special chart called “kick Chart” is used by the
mother to record her baby’s movement over a period of time.
If the fetus moves less than certain number of movements the
mother is asked to report to the clinic.
The following three criteria are the most commonly
used :
Perception of at least 10 FMs during 12 hours of
normal maternal activity
Perception of at least 10 FMs over two hours
when the mother is at rest and focused on counting
“Cardiff Count-to-Ten chart”
Perception of at least 4 FMs in one hour when
the mother is at rest and focused on counting.
DD of decreased movements “DFM”:
Transient decrease in fetal activity can be due to
fetal sleep states.
Maternal drug use (e.g. sedatives), or maternal
smoking.
Inadequate perception of movements by the
mother. E.g. early gestational age, decreased/increased
amniotic fluid volume, maternal position (sitting or standing versus
lying), fetal position (anterior position of the fetal spine), obesity,
anterior placenta, and maternal physical activity (or just being
mentally distracted).
2) Electronic Fetal Heart Rate Monitoring
Principle: Monitoring of fetal heart activities is
indirect way for assessment of fetal oxygen status.
Fetal hypoxia affects the cardiac control centers, and
result in diminished heart activities “rate, variability
and reactivates” through the autonomic nervous
system.
The technique: Electronic fetal heart monitoring depends
on recording fetal heart activities in response to uterine
contractions and or fetal movments
A Doppler ultrasound
transducer for the FH
activities
and
a
tocotransducer to detect
uterine contractions.
Fetal movements are
usually recorded by the
patient
Types antenatal fetal heart rate monitoring:
(1) The Non Stress Test “NST” and
(2)The Contraction Stress Test “CST” or
sometimes called oxytocin stress test.
Non-stress test “NST”:
The NST is the most commonly used method of
antepartum fetal assessment.
It is noninvasive (unlike the CST)
It has no direct maternal or fetal risks,
and virtually no contraindication.
Interpretation: the results of a NST is interpreted as either
reassuring or non reassuring based on criteria:
The rate of the fetal heart.
The variability “beat to beat variation”
Response to uterine contractions and/or fetal
movements:
Reassuring patterns “Reactive test”:
the following
criteria should be fulfilled over 20 minutes of fetal
monitoring:
1.A basal FHR within normal (110-160 bpm),
2.Variability range (5-25 beats),
3.At least two accelerations of the FHR of approximately
15 bpm amplitude and for 15 seconds' duration.
If these criterions are not met the test may be extended
for further 20 minutes.
Non –reassuring pattern “Non-reactive test”: The test is
labeled as non reactive if after 40 minutes the criteria for
reactivity are not met.
Reassuring patterns “Reactive test”
In some cases if the test is non-reactive,
acoustic stimulation may be used to apply a
sound stimulus for 1 to 2 seconds
(see vibroacoustic stimulation).
Interpretation of the (NST) or Cardiotocogram “ CTG
“results:
should take in consideration the gestational age (the
response of the fetal heart depends on maturation of the
fetal autonomic nervous system). Therefore it is difficult to
interpret the test before 24-26 weeks.
The presence of a reassuring pattern indicates that there
is no fetal hypoxemia only at the time of testing.
The frequency of doing the test is based on clinical
judgment and the indication for testing. It may be
performed at daily to weekly intervals as long as the
indication for testing persists.
Differential diagnosis of Non Reactive Test:
Causes other than fetal hypoxia should be considered
such as:
Benign and temporary non-reassuring test due to
fetal immaturity, maternal smoking, or fetal sleep. , or
maternal smoking.
Fetal neurological or cardiac anomalies and sepsis.
Maternal ingestion of drugs with cardiac effects.
The Contraction Stress Test “CST”
Principle:
uterine contractions cause
reduction in blood flow to the intervillous
space and transient state of hypoxia.
A fetus with inadequate placental reserve
(i.e. uteroplacental insufficiency) would
demonstrate late decelerations in response
to the transient hypoxia of uterine
The Contraction Stress Test “CST”
The Technique:
1The CST is ideally conducted in the labor and
delivery suite or in an adjacent area.
2uterine contractions is induced using oxytocin
infusion or nipple stimulation technique. The aim
is to induce at least three contractions within 10
minutes.
The Contraction Stress Test “CST”
Contraindications
patients at high risk for premature labor,
placenta previa
previous classic cesarean section or uterine surgery.
Interpretation of the Contraction Stress Test:
Negative: if no deceleration occurred during the period of
the test.
Positive: if late deceleration occur.
Vibroacoustic stimulation (VAS)
Principle: It depends on stimulation of the
fetus by an artificial burst of noise produced
by a hand-held battery-powered artificial
larynx. It generates sound pressure
levels measured at 1 m in air of 82 dB with a
frequency of 80 Hz and a harmonic of 20 to
9,000 Hz.
The goal is to alter the fetal behavioral state,
wake a sleeping fetus, and provoke
accelerations in the heart rate thus shorten
the length of the NST.
Fetal Biophysical Profile “BPP”
Fetal BPP is based on the use of real-time ultrasonography
to perform an in utero physical examination and evaluate
dynamic functions reflecting the integrity of the fetal CNS
(i.e. oxygenation)
Principle: the physical activities that reflect the biological
integrity of the fetal central nervous system include five
parameters.
Four are based on ultrasound studies include: Fetal
breathing movements (FBM), fetal body movement, fetal
tone, and amniotic fluid volume and
The fifth is the result of NST.
Fetal Biophysical Profile “BPP”
It is important to realize the following:
The presence of all the parameters is sign of healthy and welloxygenated system.
As the number of absent parameter increases, the likelihood of fetal
compromise (hypoxia) increases.
The fetal biophysical activities that appear earliest in fetal
development are the last to disappear
Appear
The Fetal Tone And Movements: (Between 7 -9 Weeks)
Fetal Heart Reactivity: The Parasympathetic then the
sympathetic system.
The Breathing Movements: Are Controlled By The
Breathing Center In Brain Stem. Breathing Movements
Start To Appear From Early Second Trimester.
Dis-Appear
Fetal Biophysical Profile “BPP”
Diminished Amniotic fluid volume “oligohydramnios”
reflects long-term fetal (Chronic) hypoxia since it
results from diminished fetal urine output. This takes
place secondary to compensatory redistribution of
fetal circulation.
The Other parameters reflect hypoxia and stress
at the time of the test
Fetal Biophysical Profile “BPP”:
The Technique:
Ultrasound examination is used to study the 4
parameters of the BPP i.e. amniotic fluid
assessment, fetal breathing movements, fetal gross
body movements, and fetal tone.
The examination is usually carried out over 30
minutes.
Interpretation of the BPP “The Fetal BPP
Score”
Each of the five parameters of the BPP is awarded 2
points.
The highest score a fetus can receive is 10, if all
parameters are satisfactory.
The lower the score the higher the risk of fetal
compromise, fetal hypoxia and acidosis
Relation between BPP Score and the Fetal Cord PH at Birth
A score of 8 or more is interpreted as normal with a very
little risk of fetal death within 1 week (estimated as <1 in a
1,000).
A score of 6 out of 10 may A repeat test should be
undertaken or delivery if the fetus is at term.
A score of 4 out of 10 should raise serious concern of fetal
compromise, with a high risk of fetal death, such that delivery
would be indicated in most situations.
A score of 0 to 2 out of 10 is an emergency and delivery
should occur depending on the clinical circumstance.
Fetal Biophysical Profile “BPP”
Principle of The Modified BPP: Because FHR accelerations
are one of the last of biophysical variables to develop,
therefore if the NST is reactive, then the other variables
should be present.
Also adequate amniotic fluid usually indicates that the fetus
is not suffering from chronic placental insufficiency.
The modified BPP is considered normal if the fluid volume is
adequate (AFI greater than 5 cm) with a reactive NST.
The modified BPP has the advantages that it takes less time
Doppler Ultrasound
Principle: Doppler ultrasound is a noninvasive
assessment of the blood flow in the fetal,
maternal, and placental circulations.
Various blood vessels have been investigated
using Doppler velocimetry, including the
maternal uterine artery, fetal middle cerebral
artery, and fetal ductus venosus
Doppler Ultrasound
In normal pregnancy the placental
vascular resistance decreases as the
pregnancy progresses, hence the
umbilical blood flow increases.
Doppler Ultrasound
In cases with placental insufficiency e.g. pre-eclampsia, or
FGR (fetal growth restriction) the Doppler blood flow study
shows decreased blood flow especially during diastole.
The fetus would also try to compensate by compensate by
shunting most of the blood flow to the brain, heart, and
adrenal glands at the expense of the placenta and
peripheral circulation, a phenomena known as “ brainsparing reflex”.
Therefore the Doppler blood flow study of cerebral vessels
would show increase in blood flow in the fetal cerebral
circulation.
Doppler Ultrasound
The technique: Doppler hemodynamic blood flow study
is based on directing beam of ultrasound waves with a
particular frequency on to the desired blood vessel.
The beam returns with different frequency proportional
to the speed and direction of flow of the blood cells in
the studied vessel.
The difference between the frequency of the emitted
beam and the frequency of the returned beam is known
as the “Doppler shift” that reflects the blood flow
velocity, and can be recorded and displayed electronically.
Doppler Ultrasound
Interpretation of Doppler Ultrasound:
an increased difference between the peak blood flow during
systole and during diastole reflect increased placenta resistance.
In severe cases there may be no flow during diastole or ever a
reversal of blood flow during the diastolic phase of the cardiac
cycle.
Normal blood flow notice
S/D ratio is a positive
Absent end diastolic blood
flow
Reversed end diastolic blood
flow