Assessment
of fetal
wellbeing
By
Dr. Khattab KAEO
Prof. of Obstetrics and Gynaecology
Faculty of Medicine, Al-Azhar University,
Damietta
Indications for fetal wellbeing surveillance
Many cases of medical
disorders.
Prolonged pregnancy:
>10 days after the
EDD or earlier in older
mothers.
Reduced fetal
movements.
Cardiff count-to-ten:
The patient begins to count movements
at 8 AM daily and marks the 1/2 h at
which the 10th movement is felt.
If 10 movements are not felt by 8 PM or
if it takes twice to feel 10 movements as
on prior days, the physician is noted.
In another opinion, notification is
indicated if there is no movement for 1
day or
if <10 movements are felt on 2 days.
Cases with reduced fetal movements are
referred for CTG tracing.
Symphysis-fundal height (SFH):
Using a non-stretchable tape, the
fundal height is measured from the
upper border of the symphysis
pubis.
From the 24th week of gestation
this measurement follows "the rule
of thumb" i.e. the fundal height in
centimetres (cm) corresponds to
gestational age in weeks. In a
normally-progressing
pregnancy
SFH measures 30 cm at 30 weeks,
34 cm at 34 weeks....
Biophysical profile (BPP): Constituents:
-3 gross FMs in 30 min.
Simultaneous limb and trunk
movements are counted as a
single movement.
- Fetal tone is exemplified by
prompt return to flexion after
extension of the limbs or trunk.
Other examples include arching,
kicking and opening and closing
of the hands.
-Continuous breathing movements
(movement of chest &
abdominal wall) for 30 seconds
at least once in 30 min.
Principles:
- If the normal NST findings are not obtained
within 20 min, test time is extended to 40 min.
- Due to fetal cycles of activity-inactivity (20-40
min), it is advisable to have a meal 1-2 hours
before testing.
- Frequency of testing depends on the clinical
situation and varies from daily to weekly testing.
- BPP is useful from 28 weeks onwards. The
earliest we begin testing is at 26 weeks.
- The principle is that different sites in the fetal
brain control different biophysical events. FMs,
fetal tone, FBMs & CTG are markers of acute fetal
asphyxia, while amniotic fluid volume is a marker
of chronic hypoxia.
- The first marks to go in case of fetal hypoxia are
breathing and FHR reactivity, and the last to go
are movements and tone.
Interpretation: Each parameter scores either 2 or 0.
- With a score of 8-10 intervention is not indicated, un
less for clinical reasons & the test is repeated weekly
- A score of 6 is equivocal. Intervention is advised if
the fetus is mature; if not, re-test within 24 h.
- With a score of <6 the relative risk of fetal or NN
death is increased by 6-x. A score of <6 could be
reassuring provided there is no oligohydramnios.
- A score of 4 is associated with a PNMR of 90/1000.
- A score of <4 in a mature fetus is an indication of
immediate delivery. If the fetus is immature, this
constitutes a real dilemma. The decision could be
immediate delivery, delivery preceded by steroidinduced lung maturation, or further fetal assessment
by prolonged NST or CST depending on the clinical
situation and the degree of fetal immaturity.
- The incidence of false -ve rate = 0.8/1000 i.e.
the test has a high predictive value –within a
week- for good perinatal outcome when the
result is normal. In contrary, the false +ve rate
for abnormal NST or abnormal FBMs is >80%
for poor perinatal outcome and >95% for PND.
BPP is affected by factors which suppress the
CNS such as hypoxia, infection & medication.
- With an abnormal score, the possibility of
neurological dysfunction should be considered.
- The test is time-consuming and provides little
additional information. It has now been superseded by CTG&amniotic fluid vol (modified BPP)
and growth assessment.
- In modern evidence-based obstetrics BPP has
been classified as care of unknown effectiveness
Cardiotocography (CTG)
Scaling is recommended at 3 cm/min paper speed.
Definitions: Baseline FHR: 110-150 bpm according to
the FIGO classification. It is the modal characteristics
that prevail apart from periodic accelerations or decelerations. It decreases 24 bpm between 16 weeks
and term (1bpm/w) due to maturation of vagal tone
Rate is rounded to increments of 5 bpm during a 10min segment. The minimum interpretable baseline
duration must be 2 min.
Long-term variability is oscillatory changes
that occur over 1 min; 5-25 bpm. It may be reduced
for up to 30 min (or even absent) due to fetal sleep
or drugs (diazepam). However, the most important
cause is fetal hypoxia. Variability is regulated by the
sinoaortal node.
Short-term variability is taken from 1 beat
[or R wave] to the next, so it is most reliably determined with a scalp electrode.
Reduced variability is the most reliable sign of fetal
compromise.
Bradycardia: <100 bpm for
>3 min (according to FIGO;
<110 bpm according to
ACOG). It could be due to
drugs (like -blockers) or
congenital fetal heart block.
However, it could be due to
fetal distress.
Tachycardia: >150 bpm (according to
FIGO; >160 bpm according to ACOG). It
could be idiopathic, or due to drugs (like
atropine & mimetics), fever, maternal
or fetal hyperthyroid., maternal or fetal
anaemia or prematurity. However, it
could be due to fetal distress.
Sinusoidal pattern: Type I (saw tooth)
with almost fixed variability. It is benign
Type II with smooth sine wave
& a regular frequency of <6 cycles/min
and an amplitude of >10 bpm. It is preterminal. It is seen with serious fetal
anemia of D-iso-immunisation, ruptured
vasa previa & twin-to-twin transfusion.
Differential diagnosis is effect of drugs
like morphine, alphaprodine and butorphanol
Deceleration
Gradual fall in FHR by ≥15 bpm for ≥15
sec. It is stimulated by
chemoreceptors.
Early deceleration: The nadir occurs ≤20
sec of the peak of contraction; now:
30 sec after the onset of contraction).
The waveform is symmetrical. Early
deceleration is the result of head
compression during uterine contrac.
which probably causes vagal nerve
activation. It is not associated with
hypoxia, acidemia or low Apgar scores.
This early deceleration is deemed benign because some contractions are not associated with decelera
tion, and shoulders (particularly pre-deceleration ones) are not lost. Finally, other items like baseline
FHR and variability are normal. The most right drop in FHR (white arrow) is not regarded as deceleration because the drop is <15 bpm.
Early decelerations are not always benign.
It is deemed sinister in the following conditions:
1- If associated with one of the following:
FHR <100 bpm  ineffective placental perf
Rising FHR.
Loss of long-term variability.
Loss of shouldering.
2- If unprovoked i.e. without active
uterine contractions.
3- If it is repetitive or deep.
Late deceleration
The waveform of FHR decrease shows gradual onset
and recovery and is symmetrical. Onset begins at or
after the peak of contraction. The nadir occurs >20
sec after the peak of contraction (now: 30 sec).
Return to the baseline only occurs after the contraction
has ended. This diagnosis is applicable only for 3
such decelerations following consecutive contractions
So, it can occur occasionally (reassuring signs are:
the presence of shouldering & variability, in addition
to normal baseline). Typically, depth is no >10-20
bpm (i.e. shallow). It is attributable to reduced
placental blood flow with deep ones are seen with
abruption. It more commonly occurs with maternal
hypotension and excessive uterine activity. It is
deemed sinister if deep (FHR decreases by>60 bpm)
and prolonged (persists for >60 sec).
Early and late decelerations almost reflect the shape of
uterine contraction and all dips are of almost
identical shape.
Variable decelerations
All decelerations that are not early or late.
These are the most common decelerations.
Dips are of variable shape, depth and
correlation to uterine contractions. Onset is
abrupt and nadir follows after a <30 sec
period. Duration is <2 min. Variable deceleration is attributable to compression of
the umbilical cord. It indicates fetal distress
if deep (<70bpm[signif variable deceleration)
and persistent (lasting for 60 sec with each
contraction) or associated with reduced
variability or meconium-stained liquor.
Accelerations
These are abrupt increase in FHR (>15
bpm) in response to fetal movement,
uterine contractions, cord occlusion or
fetal acoustic stimulation, stimulation
during pelvic examination or scalp blood
sampling. During labour they are nearly
always associated with fetal movement.
They are always reassuring and almost
always confirm absence of acidemia.
FIGO definition of antenatal CTG
Normal: baseline of 110-150 bpm,
variability of 5-25 bpm, ≥2
accelerations in 20 min and absence
of deceleration except for mild ones
of very short duration.
Suspicious: baseline 100-110 or 150-170
bpm, variability of 5-10 bpm for >40 min
or >25 bpm, no accelerations for >40 min
and sporadic deceleration of any type
unless severe.
Pathological: baseline of <100 or >170
bpm, variability of <5 bpm, recurring and
repeated decelerations of any type.
Limitations of CTG use
The major limitation of CTG is that fetal adaptation
results in maintenance of the FHR until death. An acute
reduction in O2 delivery produces a transient bradycardia.
However, if reduction in O2 delivery is prolonged, the
FHR returns to normal (a possible effect of catechol.),
but with a further acute reduction in O2 delivery there
will be lack of response (no reaction). In progressing
utero-placental insufficiency there would be: loss of
acceleration  deceleration  progressive reduction in
variability. The rate usually remains normal.
Also, fetal quiescence is normally associated with loss
of acceleration and low variability. A non-reactive CTG
with variability present should be continued (up to 2 h)
until fetal activity occurs or until its continued absence
indicates a problem.
FHR tracing 15% false +ve rate & 0.3% false -ve rate
In another opinion 40% of abnormal CTGs occurs in the
absence of fetal hypoxia; CS rate will be trebled if CTGs
are used alone. Even with the most severely abnormal
CTG, the fetus will be hypoxic in only half the cases.
Normal CTG is insufficiently reassuring in at-risk cases.
Non-stress test (NST)
The test correlates FHR response to fetal
movements. If no fetal movement felt within
20 min, the test is extended for 20 min more,
perhaps after acoustic stimulation.
The woman is put in the semi-Fowler position
with a lateral tilt.
Two accelerations (↑ in FHR by >15 bpm for
>15 sec) within 20 min = "reactive". If this is
not achieved within 20 min, the test is
deemed "non-reactive". The incidence of false
positive rate = 3/1000. The incidence of false
negative rate = 3/1000.
Absence of acceleration may indicate hypoxia.
Deceleration with Braxton-Hicks contractions
(unstress test) indicates oxygen insufficiency
and requires urgent investigation.
Contraction stress test (CST)
The test time is 90 min.
Uterine contractions are induced and
maintained at a rate of 3/10 min.
The test is deemed "positive" if there are
persistent late decelerations with >50% of
the contractions. "equivocal" if late decelerations are occasional. "negative" if there
is no late deceleration.
The incidence of false negative rate =1/1000
If negative, the test is repeated weekly. If
positive, a complete BPP is recommended.
The test is contraindicated if there is a
previous uterine scar or threatened preterm
labour.
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