Fetal Non Stress Test - What Is It & Why Is It Done
The Fetal Non-Stress test is a simple and non-invasive test which is usually performed
once you have progressed past the 28 week mark. This test – as the name suggested
– does not put your baby under any stress at all.
How is a Non-Stress Test Performed?
The test can take anywhere between 20 – 60 minutes to be complete. During the test
you will be made to lie on your left side – sometimes with a wedge under your back
that allows you to lean back. An assistant will strap two devices to your belly:
One monitors your baby's heartbeat and movement and the other records contractions
in your uterus. The assistant then listens to and watches your baby's heartbeat
on an electronic screen while your contractions are recorded on paper.
Why would a NST be performed?
Your health care provider may want to perform a non stress test
if:
 You sense that the baby is not moving as frequently as usual
You are overdue
There is any reason to suspect that the Placenta is not functioning adequately
You are considered a High risk pregnancy
The test can indicate if the baby is
not receiving enough oxygen because of placental or umbilical cord problems or other
types of fetal distress.
The non stress test also allows your health care provider
to measure the heart rate of your baby in response to its own movements. Healthy
babies will respond with an increased heart rate during times of movement and the
heart rate will decrease at rest.
What do the results mean?
If your baby's heartbeats while he/she is moving for at least 15 seconds on two separate occasions during
a 20-minute span then the result is normal, or "reactive." A normal result means
that your baby is probably doing fine. Your practitioner may want to repeat the
test every week (or more often) until your baby's born – this usually depends on
why you are needing this test performed and how serious the cause is.
If your baby's
heart doesn't beat faster while he's moving or your baby doesn't move after about
90 minutes, then result is "nonreactive." A nonreactive result doesn't necessarily
mean something is wrong. It just means that the test didn't provide enough information.
This usually means that the test will need to be done again in an hour or so, or
your health care provider may choose to perform other tests.
A nonreactive result
could also indicate that your baby isn't getting enough oxygen or that there are
problems with the placenta. A nonreactive non-stress result requires additional
testing to determine whether the result is truly due to poor oxygenation, or whether
there are other reasons for fetal nonreactivity (i.e. sleep patterns, certain maternal
prescription or nonprescription drugs).
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