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
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