Antepartum Fetal Surveillance
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Pathophysiology:
-Hypoxemia
-> acidemia -> FHR pattern, activity
level, and muscular tone
-> diminished renal perfusion ->
oligohydramnios
Role:
-To predict fetal hypoxemia or acidemia.
-It does not predict acute, catastrophic changes such as
placental abruption or placental cord accidents.
-Does not predict severity or duration of abnormality
-Highly reassuring: Low false negative rate – a normal test
means the chance of a stillbirth in the next ~1wk is unlikely
-When corrected for congenital
anomalies and unpredictable (acute) causes, rates are between 0.3 (CST) and 1.9
(NST) /1000.
-Observed lower rates of fetal death vs untested (and
presumably lower-risk) as well as historical controls.
-No good
RCTs because you can’t randomize someone to no surveillance
1)
Indications
a.
Maternal
i. cHTN,
DM, AMA, SLE/APAS, Hyperthyroidism, CRD, Hemoglobinopathies, Cyanotic heart
disease, previous fetal demise
b.
Fetal
i. Growth
Restriction, Decreased FM, TTTS or significant growth discrepancy
c.
Pregnancy-related
i. PreE,
gHTN, gDM, oligo, late/postterm pregnancy, isoimmunization
2)
Fetal Surveillance Techniques
a.
Maternal-Fetal Movement Assessment “Kick Counts”
i. Decrease
in perception of movements may precede death, sometimes by days
ii. Optimal
regimen not established
1.
10 movements over 2 hrs
2.
1hr x3/wk to establish baseline, then compare to
it
b.
Non-Stress Test (NST)
i. FHR
of fetus that is not acidotic or neurologically depressed will temporarily
accelerate
ii. Position
patient with head of bed elevated 30 degrees or lateral recumbent position
iii. Monitor
for 20min at a minimum, but may require 40min to account for sleep-wake cycles
1.
Vibroacoustic stimulation is valid
a.
Reduces frequency of nonreactive NST by 40% and
overall testing time by ~7min without compromising test
b.
Applied 1-2 seconds; may be repeated up to 3
times up to 3 seconds each
iv. Results
1.
Reactive
a. >=2
accels in 20min
2.
Non-reactive
a.
<2 accels in 40min
3.
Non-reassuring
a.
Repetitive decelerations: a/w increased risk of
nonreassuring intrapartum FHR patterns or fetal demise
c.
Biophysical Profile (BPP)
i. NST
plus ultrasound; 30 minutes to complete.
1.
Fetal breathing movements
a.
Rhythmic breathing episode >30s
2.
Movements
a. >=3
discrete body/limb movements
3.
Tone
a. >=1
episode of flexion/extension
4.
Amniotic Fluid Assessment
a.
MVP <2cm
is considered oligohydramnios, and should also prompt investigation
i. AFI <5cm also oligohydramnios
ii. MVP
is a/w reduction in unnecessary interventions without increase in adverse
perinatal outcomes
5.
NST
ii. Results:
Out of 10; each category 2pts each
1.
8 or 10: Normal
2.
6: Equivocal
3.
0-4: Abnormal
d.
Modified Biophysical Profile
i. NST
plus amniotic fluid assessment
ii. Results
1.
Normal: Both reactive NST and MVP³2cm
e.
Contraction Stress Test (CST)
i. Fetal
oxygenation is transiently worsened by ctx; if fetus not well oxygenated à late decels
ii. Place
patient lateral recumbent position
iii. Adequate
contractions ³3 ctx
>40s /10min
1.
Induced via nipple stimulation or IV oxytocin
iv. Results
1.
Unsatisfactory: <3ctx in 10min, or
uninterpretable tracing
2.
Negative: no late or variable decels
3.
Equivocal: decels that occur during tachysystole
(>ctx/2min) or prolonged ctx >90s
4.
Equivocal-Suspicious: Late decels <50% ctx,
or significant variable decels
5.
Positive: Late decels >50% ctx (even if
unsatisfactory)
v. Contraindications:
Vaginal Delivery.
f.
Umbilical Artery Doppler Velocimetry
i. Pathophysiology:
Poor placenta function and placental small artery obliteration à increased resistance à decreased in umbilical
artery flow
1.
May become absent or reverse
ii. Measurement
1.
Common Indices
a.
S: Systolic flow; D: Diastolic flow; A: Average
b.
Systolic:Diastolic Ratio: S/D
c.
Resistance Index: S-D/S
d.
Pulsatility Index: S-D/A
iii. Use
1.
Evidence exists for use in growth restricted
fetuses
2.
No evidence for use in fetus without growth
restriction
iv. No
benefit to other vessel measurements
1.
Middle cerebral artery
2.
Precordial venous system
3)
Frequency
a.
If indication for testing resolves, no further
testing needed
b.
If persistent, repeat periodically
i. Typically
weekly, although should be individualized as the optimal is unknown
c.
Growth Restriction
i. If
growth is a concern, growth U/S q3-4wks appropriate
4)
Delivery considerations (if abnormal results on
surveillance)
a.
Factors
i. GA
– Risk of neonatal complications
ii. Risk
of fetal demise
iii. Severity
of maternal condition
b.
False Positive: In one large center study, 60%
of infants delivered for abnormal antepartum testing had no e/o short or
long-term fetal compromise
5)
Management of Abnormal Results
a.
Consider context
i. May
resolve if maternal condition improves
b.
Beware a positive test: Low PPV
i. Follow
decreased FM with an NST, or a nonreactive NST with a BPP
1.
8-10: Reassuring
2.
6: >37+0, consider delivery; <37+0, repeat
BPP in 24hrs
3.
0-4: usually indicated delivery is warranted
a.
If <32+0 individualize management and
consider extended monitoring
ii. UA
Dopplers
1.
Use only in growth restricted fetuses
2.
No good studies, recs:
a.
REDF: Delivery >32+0
b.
AEDF: Delivery >34+0
c.
If S:D ratio elevated, but diastolic flow
present, may consider delivery >37+0
3.
IOL with continuous monitoring is acceptable
c.
Oligohydramnios
i. Assess
if membranes have ruptured
ii. Otherwise
uncomplicated, isolated and persistent oligohydramnios:
1.
Delivery at 36+0-37+0
2.
If <36+0, individualize.
a.
If not delivered, f/u amniotic fluid
assessments, NSTs, fetal growth assessments.
In this graphic, the large upward peaks represent forward flow during systole. The troughs represent flow during diastole. In a normal fetus, with a normal placenta, there is forward flow during the fetal cardiac diastole (A). However, with a poor placenta causing increased resistance, there may be absent (B) or reversed (C) flow during diastole.
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