A nonstress test monitors an unborn baby's heart rate for 20 to 30 minutes to see if it changes as the fetus moves and during contractions. It is called "nonstress" because doing it places no stress on the fetus.
Why Are Nonstress Tests Done?
A nonstress test (NST) is usually done when a health care provider wants to check on the health of the fetus, such as in a high-risk pregnancy or when the due date has passed.
The test checks to see if the baby responds normally to stimulation and is getting enough oxygen. A baby that doesn't respond isn't necessarily in danger, though more testing might be needed.
Sometimes, a biophysical profile (BPP) is done, which includes an ultrasound and an NST. A BPP examines a baby's breathing, movement, amount of amniotic fluid, and tone, in addition to the heart rate response.
Should I Have a Nonstress Test?
Your health care provider may recommend this if you have a high-risk pregnancy, if there are concerns during your pregnancy, or if you have a low-risk pregnancy but are past your due date.
What Happens During a Nonstress Test?
You'll wear two monitors (one tracks the baby's heartbeat and movement, and the other records contractions) while lying on your left side. A technician monitors the fetal heart rate during each movement on a screen while your contractions are recorded on paper.
If there's no movement during the test, the baby may be asleep and the technician may use a buzzer to wake the baby. You also may be asked to drink or eat to try to stimulate the baby more.
When Are Nonstress Tests Done?
A nonstress test is done any time after 26 to 28 weeks, depending on why it's needed. This is the age when a baby's heart rate can respond to movements by speeding up or slowing down.