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I. Objectives
A. Physiologic and technologic principles of antepartum fetal heart rate testing (AFHRT)
B. Application and interpretation of AFHRT
C. Areas of controversy and testing pitfalls
II. Fetal movement (FM) Counting
A. Physiologic background
1. Healthy fetuses move 20-30 times per hour
2. Fetal movement occupies 10-15% of 24h day
3. Active fetus has high likelihood of good result
4. Feud compromise may follow' decreased FMs
B. Basis for maternal perception fion of F'M
1. Inexpensive, simple No equipment needed
3. May be done in home, office, hospital
4. Patient is engaged in her care process
C. Application
1. Each fetus acts as own control
2. Baseline record of activity can be established fetal heart rate
3. Clinical alerts: decreased or absent Fms
4. Note: same conditions for each session
D. Follow up
1. Supplement other forms of testing
2. Decreased FM _ more intensive testing
3. NOTE: inform patient that absolute FM count may vary considerably between sessions
E. Limitations
1. Limited numbers of good clinical trials
2. Low sensitivity to prediction of acute distress
3. Normal "slow" or "hyperactive" fetus?
4. Variation m patient educability compliance
III. Principles: Physiologic Bases
A. Fetal heart rate testing: applications
1. NST: office/hospital possibly home. 20-30 min to t-2 h
2. VAS' similar to NST. 10-20 min
3. ACTG: similar to NST CST: office/hospital. 20-30 min to 2-3 h
B. Nonstress test (NS'I)
1. What does the NST test?
a) Selected FHR baseline features
(1) Accelerations with FMs (O)
(2) Baseline rate and variability (?)
(3) Decelerations: spontaneous (O)
b) Physiologic
c) Pathophysiologic
d) Brainstem function
e) Hypoxia./acidosis
f) ANS/reflex control
g) Malnutrition
h) Maturation of FHR
i) Cord compression
j) Circadian rhythms
k) Placental insufficiency
1) Behavioral state
m) CV and CNS anomalies
2. Physiologic basis for NST
a) FM is normal, episodic phenomenon
b) Third trimester fetuses respond to FM with coupled accelerations (>90%)
c) Hypoxia, asphyxia, malnutrition reduce FMs. decrease coupling fewer accelerations
3. NST interpretation
a) Reactive: accelerations + Fms
b) Nonreactive
(1) Accelerations present, too few
(2) Accelerations absent. FMs present
(3) Accelerations, FMs absent
4. Nonreactivity sequence
a) Decreased acceleration counts, amplitude
b) Decreased FM counts
c) Uncoupling accelerations and Fms
d) No accelerations or Fms
e) Spontaneous decelerations
5. Causes of nonreactive NST
a) Compromised fetus
b) Behavioral state
c) Immaturity
d) Maternal diet/drugs
e) Fetal anomalies
6. Testing conditions
a) Length of observation: 30'-60' needed for 1 acceleration m 95%. of
normal fetuses
b) Devoe, McKinzie, et al. Am JOb G?n 1985
(1) Reactivity in 95% within 70 minutes
(2) Nonreactivity (>90') ~ abnl CST (95 %)