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Acceleration
A visually apparent
increase (onset to peak in less than 30 sec) in the FHR from the most
recently calculated baseline
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The duration of an acceleration is defined as the time from the initial
change in FHR from the baseline to the return of the FHR to the baseline
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At 32 weeks of gestation and beyond, an acceleration has an acme of 15
beats per min or more above baseline, with a duration of 15 sec or more
but less than 2 min
- Before 32 weeks of gestation, an acceleration
has an acme of 10 beats per min or more above baseline, with a duration
of 10 sec or more but less than 2 min
- Prolonged acceleration lasts 2 min or more, but less than 10 min
- If an acceleration lasts 10 min or longer, it is a baseline change
(NICHD)
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Accelerations
of
the FHR may be periodic (that is, occurring in relation to a
contraction) or episodic (no association with a contraction). Most are
episodic. These episodic accelerations are generally in response to
fetal movement, with a need for increased perfusion, and therefore
transiently increased sympathetic tone, or due to fetal stimulation,
such as scalp stimulation with a vaginal exam, abdominal palpation, or
vibroacoustic stimulation.
Periodic accelerations are those
associated with uterine contractions and may be due either to fetal
stimulation (particularly in breech presentation) or due to mild cord
compression (that is, compression of the umbilical vein only).
FHR
accelerations and good (moderate) variability are closely associated
and sometimes may be visually indistinguishable, though both are
reflective of a well-oxygenated fetus.
The presence of
accelerations forms the basis of the nonstress test (NST). An NST is
said to be reactive when there are at least two accelerations in a 20
minute period, along with moderate variability and no decelerations.
Below is an example of fetal acceleration. Please click to
enlarge.
 Acceleration Video 1
Acceleration Video 2
Acceleration Video 3
Acceleration Video 4
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