Fetal movements translate to fetal
well-being. Of course there are times
when the fetus is not active and this
does not necessarily imply that the
fetus is in trouble. For instance
it is normal for the fetus to move
less towards the end of the term because
there is less room for movement. There
are also situations when due to extra
amniotic fluid the mother is not able
to feel the movements. To be on the
safe side, contact your care provider
if you notice movements have decreased
considerably. Tests will be carried
out to analyze the baby's well being.
One such test is the CST or contraction
stress test.
What
is CST..
• CST is based on the observation
that during contractions, blood
flow to the placenta lessens temporarily.
An evaluation is done on how the
fetus handles this stress.
• Normally fetal heart rate is not
affected by contractions
• In actual labor after contraction
begins, if the fetal heart beat
slows down, it indicates that the
fetal is not able to tolerate the
decreased blood flow resulting from
the contraction.
• These decreases are called
late
decelerations .
• If the placenta is not working to
capacity or the baby has some problem,
Contraction can decrease the oxygen
flow and cause the heart rate to
drop.
• CST is used if nonstress test showed
no change in the fetal heart rate
when the fetal moved
• The logic behind the test is to
challenge the fetus with contractions
for brief periods to see if the
fetal heart demonstrated decreases.
Positive test usually indicates
that the fetus needs to be delivered
The
Procedure itself..
• Two fetal monitors will
be strapped to the woman's abdomen
to record fetal heart rate. She
will lie on her left side
• It is usually conducted if the pregnant
woman has had problematic pregnancies
in the past or has medical problems
in her current pregnancy.
• CST is usually performed if nonstress
test wasn't reassuring in the last
few weeks of pregnancy
• One monitor will pick up uterine
contractions and the other picks
up fetal heart beat. Both will readings
will record on graph paper
• The heart beat will form a line
at the top and the maternal contractions
will form wavelike lines at the
bottom. Both lines will be matched
to determine the significance of
any decelerations
• Contractions are either induced
with oxytocin, a hormone usually
used to induce labor. It is given
through an IV line. Before this
the baseline heart beat will be
recorded for about 20 minutes max
• In place of oxytocin, nipple stimulation
can also be used to induce natural
oxytocin in the system. The mother
will be asked to rub her nipple
for about 15 minutes until adequate
contractions have been achieved.
• The plus side of nipple stimulation
is contractions are induced more
quickly and an IV is not required
• Either way the responses are obtained
and recorded
• Three contractions must take place
in the 10 minute duration and each
contraction must last for about
40 seconds. This is regarded as
the approximate stress the fetus
will endure during labor
• The test can last for a good 2 hours
Result
Interpretations..
The possible interpretations of CST
are:
•
Negative - this
is the desired result. It implies
that no late decelerations are present
in the presence of adequate contractions,
the placenta is functioning properly
and the fetus will be doing fine for
at least a week. In high risk pregnancies
CST will have to be performed more
than once a week
•
Positive late decelerations
are obvious in the presence of adequate
contractions. Delivery of baby follows
a positive result either by induction
of labor or C-section, whichever appropriate
•
Suspicious the late
decelerations are not consistent.
A suspicious CST requires a repeat
of test usually within the same day
or 24 hours
•
Hyperstimulation
CST showing contractions are happening
too frequently (5 or more in 10 minutes)
or its lasting too long (90 seconds
or more). Hyperstimulated test is
considered negative if decelerations
are absent; it can be considered invalid
if decelerations do occur. CST should
be repeated in 24 hours
•
Unsatisfactory fetal
heart rate cannot be traced or the
desired contractions (3 in 10 minutes)
cannot be achieved. CST should be
repeated in 24 hours
Fortunately there are very, very few
incidence of false negative' results.
Essentially a
false negative
result will show the fetus is faring
well when in actual fact it is in
distress
