Fetal non-stress test
The stress-free fetal test is
a simple, non-invasive test that is performed at gestational age greater than
28 weeks. The test is called "stress-free" because the fetus is not
stressed during the test.
How is a non-stress test performed?
The test involves attaching a
strap to the mother's abdomen to measure the fetal heart rate and another strap
to measure contractions. Movement, heart rate, and heart rate
"response" to movement are measured over 20 to 30 minutes. If the
baby is not moving, this does not necessarily indicate a problem; the baby can
just sleep.
The nurse may use a small
"buzzer" to wake the child up for the remainder of the test.
Why would a non-stress test be performed?
A stress test can be done if:
- You sense the baby is not moving as frequently as usual
- You are overdue
- There is any reason to suspect the placenta is not functioning adequately
- You are high risk for any other reason
The test can determine if the
baby is not getting enough oxygen due to problems with the placenta or
umbilical cord; it may also indicate other types of fetal distress.
What are the risks and side effects for the mother or baby?
The stress-free test is a
non-invasive test that has no known risks or side effects for the mother or
baby.
When is a non-stress test done?
Non-stress tests are usually
done after 28 weeks of pregnancy. Before 28 weeks, the fetus is not
sufficiently developed to respond to the test protocol.
What is a non-stress test looking for?
The main purpose of the test
is to measure the fetal heart rate in response to its own movements. Healthy
children respond with an increase in heart rate during periods of movement, and
at rest, the heart rate decreases. The concept of a stress-free test is that
sufficient oxygen is needed to keep the fetus active and the heart rate within
normal limits.
When oxygen levels are low,
the fetus may not respond normally. Low oxygen levels can often be caused by
problems with the placenta or umbilical cord.
What do the results of the
non-stress test mean and what are the reasons for further testing?
A reactive stress-free result indicates adequate blood (and oxygen) flow to the fetus. A stress-free non-response result warrants further testing to determine if the result is indeed due to poor oxygenation or if there are other reasons for the fetal non-response (sleep, certain prescription or over-the-counter medications for the mother free of charge).