Antenatal Fetal Assessment Flashcards
goal of evidence-based antepartum fetal evaluation?
To decrease :
●perinatal mortality
●permanent neurologic injury
Causes of still birth
Asphyxia (IUGR, prolonged gestation) =>in about 30%
Maternal complications (placental abruption, hypertension, preeclampsia, and
diabetes mellitus) => in about 30%
Congenital malformations and chromosome abnormalities => in about 15%
Infections => 5%
No obvious fetal, placental, maternal, or obstetric etiology => in about 20%
o this percentage increases with advancing gestational age
Normal fetal states
- State 1F [quite sleep state]
- State 2F [active sleep state]
- State 3F
- State 4F [awake state]
State 1F
Fetus spends 25% of its time
Narrow oscillation of FHR
Slow FHR, reduced variability
Can last 20Min
● can be affected by activity, drugs & nutritional status
State 2F
Fetus spends 60-70% of its time
Frequent gross movement.
wider oscillation of FHR,
Continuous eye movement,
Increase variability, and Increase
acceleration with FM
Can last 40min
● can be affected by activity, drugs & nutritional status
State 3F
Continues eye movement in the
absence of FM
No acceleration of FHR with
movement
Existence is questioned
State IV
Vigorous body movement
Continues eye movement
FHR acceleration and inc variability
mechanisms that control these periods of rest and activity in the fetus maybe
●mother’s activity
●her ingestion of drugs
●her nutrition
At term
fetal anomalies, particularly central nervous system (CNS) anomalies;
maternal exposures, including corticosteroids, sedatives, smoking, and anxiety;
low amniotic fluid volume; and
decreased placental blood flow due to placental insufficiency
Fetal movement
Fetal movement is a more indirect indicator of fetal oxygen status and CNS function,
and decreased fetal movement is noted in response to hypoxemia.
However, gestational development of fetal movement must be considered when
evaluating fetal well-being as marked by fetal activity.
o Periods of absent fetal movement become more prolonged as gestation
advances,
How to stimulate fetal movement
VAS [Vibro-Acoustic Stimulation]
Indications for testing
●Pregnancy related
GH / PE
Decreased fetal movement
Gestational diabetes mellitus (poorly
controlled or medically treated)
Oligohydramnios
IUGR
Late term or postterm pregnancy
Isoimmunization
Previous fetal demise (unexplained
or recurrent risk)
Monochorionic MG (with significant
growth discrepancy)
● maternal related
Pregestational DM
Hypertension
SLE
Chronic renal disease
Antiphospholipid syndrome
Hyperthyroidism (poorly controlled)
Hemoglobinopathies (sickle cell,
sickle cell– hemoglobin C, or sickle
cell–thalassemia disease)
Cyanotic heart disease
Frequency of testing
If maternal med condition is stable, & tests are reassuring
●weekly
If there is high risk condition
● more frequently
Modalities of antepartum testing
Fetal movement count
Non stress testing
Contraction stress testing
Biophysical profile
Modified biophysical profile
Doppler Velocimetry
How many percent of the times a fetus makes gross body movements in 3rd tmx and how many times /hr on average??
10% of the time
3 mvts/hr
Duration of active fetal movement
40 min
Duration of Quite periods
20 min
At what time does the fetal movement peaks❓️
9:00pm & 1:00am , a time when
maternal glucose levels are falling
The longest period without fetal movement?
75min
How many percent of the fetal movement does the mother perceives?
70-80%
Maternal factors that may influence the evaluation of fetal movement include
maternal activity
parity
obesity
medications
psychological factors including anxiety
Methods of FM counting
- The Cardiff “count-to-10” methods [used frequently]
● mother count FM once/day
(6am to 6pm)
● <10 movement over 12 hours
is alarming - Sadovsky method
● mother count FM 2-3x daily
● <3 movement/one hour is
alarming - Rayburn method
●count once per day for
60minutes
● <3 movement/1hr for two
consecutive days is alarming
The most widely applied technique for antepartum fetal evaluation?
Non-Stress Test
FHR acceleration
increment in FHR by 15bpm from the baseline and
lasts for 15seconds
What does NST tell us?
That the ANS of the fetus is functional
In what state would the FHR acceleration be absent?
Quite fetal sleep
●Maximum period for absence of FHR acceleration still be normal is
~80min.
Findings of NST
- Reactive NST- 85% of cases
● At least two accelerations of FHR by 15bpm above the baseline which lasts
for 15sec in 20min of observation in those above 32wks of gestation.
● At least two accelerations of FHR by 10bpm above the baseline which lasts
for 10sec in 20mins of observation in those less than 32 weeks of gestation - Non-reactive NST- 15% of cases
● If less than two accelerations in 20 minutes
Factors causing non reactivity
- Quite sleep state
- Beta blockers, narcotics, sedatives, phenobarbital, alcohol
- Chronic smoking
Mgt of non reactive NST
Prolong duration of test to 40min
Do Vibroacoustic stimulation (VAS)
• Use of sound wave to stimulate FM
• It shortens observation time
• Interpretation is the same
Do CST or BPP
What is the first biophysical technique widely applied for antepartum fetal
surveillance?
Contraction Stress Test (CST) AKA Oxytocin Challenge Test (OCT)
What does CST tells us?
response of the FHR to uterine contractions
Mechanism of CST
fetal oxygenation will be transiently worsened by uterine contractions, leading to the FHR pattern of late decelerations
Late deceleration
visually apparent and usually symmetrical gradual decrease and return to baseline of FHR in association with uterine contractions, with the time from onset of the deceleration to its FHR nadir as 30 seconds or longer
How to do CST?
An adequate CST requires uterine contractions of moderate intensity that last about 40 to 60 sec with a frequency of three in 10 minutes.
o These criteria were selected to approximate the stress experienced by the fetus during the first stage of labor.
o If uterine activity is absent or inadequate,
● intravenous oxytocin is begun to initiate contractions, and it is
increased until adequate uterine contractions have been achieved
● nipple stimulation has been used to induce adequate uterine activity,
and the success rate at achieving adequate contractions and test
results is comparable to that of oxytocin infusion
Contraindications of CST
1.Patient at high risk for premature labor,
PROM
multiple gestations
cervical incompetence,
2. The CST should also be avoided in conditions in which uterine contractions may be dangerous,
placenta previa
previous classic cesarean delivery
uterine surgery
Interpretation of CST findings
1.Negative
● No late decelerations appear anywhere on the tracing with adequate uterine contractions (three in 10 min)
2. Positive
● Late decelerations that are consistent and persistent present with the majority (>50%) of contractions
without excessive uterine activity; if persistent late decelerations are seen before the frequency of contractions is adequate, the test is interpreted as positive
3. Suspicious
● Decelerations are late and inconsistent
4.Hyperstimulation
● Uterine contractions closer than every 2 min or lasting
more than 90 sec or five uterine contractions in 10 min;
if no late decelerations are seen, the test is interpreted
as negative.
5. Unsatisfactory
● The quality of the tracing is inadequate for interpretation or adequate uterine activity cannot be
achieved
Limitation of CST
High incidence of false +ve leading to unnecessary premature interventions
Factors causing +ve CST
Misinterpretation of tracing
Supine hypotension
Uterine hyperstimulation
Fetal jeopardy
Mgt of abnormal CST result
For suspicious CST, repeat the CST
For positive result do BPP
Biophysical profile BPP
1.Fetal breathing movements
2. Gross body/limb movement
3. Fetal tone
4. NST
5. Amniotic fluid volume
- Fetal breathing movement
●Score 2
At least one episode of ≥30 sec duration
in 30-min observation
●Score 0
Absent or no episode of ≥30 sec
duration in 30 min
Gross body/limb movement
● score 2
At least three discrete body/limb
movements in 30 min (episodes of active
continuous movement considered a
single movement)
● Score 0
Up to two episodes of movements
in 30 min
Fetal tone
● Score 2
At least one episode of active extension
with return-flexion of fetal limb or trunk,
with opening and closing of the hand
considered to reflect normal tone
● Score 0
Either slow extension with return partial flexion, movement of limb in full extension, or absent fetal movement
NST
●Score 2
At least two episodes of acceleration of
≥15 beats/min and 15 sec duration
associated with fetal movement in 20 min
●Score 0
Fewer than two accelerations or
acceleration <15beats/min in 20 min
Amniotic fluid volume
●Score 2
At least one pocket of amniotic fluid
measuring ≥2 cm in two perpendicular
planes
●Score 0
Either no amniotic fluid pockets or
a pocket <2 cm in two perpendicular planes
Score interpretation of BPP
●8 – 10 Normal; low risk for
chronic asphyxia
Repeat testing at weekly to twice-weekly intervals.
●6 Suspect chronic asphyxia
(Possible fetal Asphyxia)
If ≥36-37 wks gestation or <36 wk with positive
testing for fetal pulmonary maturity, consider
delivery;
if <36 wk and/or fetal pulmonary maturity testing is
negative, repeat biophysical profile in 4-6 hrs;
Deliver if oligohydramnios is present.
● 4 probable fetal asphyxia If ≥36 wk gestation, deliver; if <32 wk gestation,
repeat score.
●0 – 2 Strongly suspect chronic
asphyxia (Almost certain
fetal asphyxia)
Extend testing time-120 min; if persistent score is 4
or less, deliver regardless of gestational age.
Why is BPP modified and what does the modified BPP include?
In an attempt to simplify and reduce the time necessary to complete testing, a variety of modifications of the full BPP have been evaluated by focusing on the components of the BPP that are most predictive of perinatal outcome.
The modified BPP combines:
NST, as a short-term indicator of fetal acid–base status, with
AFV assessment, as an indicator of long-term placental function
Interpretation of modified BPP
Normal if the NST is reactive and the amniotic fluid volume is greater than 2 cm in the deepest vertical pocket and
Abnormal if either the NST is nonreactive or amniotic fluid volume in the deepest vertical pocket is 2 cm or less (i.e., oligohydramnios is present).
Doppler velocimetry
Noninvasive method to assess blood flow; based on the observation that flow
velocity waveforms in the umbilical artery of normally growing fetuses differ from those of growth-restricted fetuses.
Interpretation
Specifically, the umbilical flow velocity waveform of normally growing fetuses is characterized by high-velocity diastolic flow, whereas in growth-restricted fetuses, there is decreased umbilical artery diastolic flow
In some cases of severe fetal growth restriction, diastolic flow is absent or even reversed.
o The perinatal mortality rate in such pregnancies is significantly increased
Interpretation
Umbilical artery systolic/diastolic ratio is commonly used
Usually employed in case of IUGR: not recommended for other obstetric problems
other than IUGR
Perinatal mortality rate for absent end-diastolic flow is 10%
