Nonstress is a common test done during pregnancy to check the health of the unborn baby. It is also referred to as fetal heart rate monitoring. During this test, the heart rate of the baby is monitored to determine its response to movements of the baby. Whether you need a nonstress test or not is decided by your physician on the basis of several factors including the chances of survival of your baby if delivered before normal time, how severe your condition is and what is the risk of losing pregnancy.
Why Should You Get a Nonstress Test?
The purpose of a nonstress test is to evaluate the health of the baby before birth. Nonstress test helps by providing useful information about the oxygen supply of your baby by monitoring their heart rate and by determining the response of the heart rate to movement of the baby.
Under normal conditions, the heart of the baby beats at a faster rate while they are active during the later weeks of pregnancy. However, in certain conditions such as fetal hypoxia (lack of oxygen supply to the baby), this pathway can be disrupted.
You may be recommended by your physician to undergo a nonstress test in the following circumstances:
- Presence of multiple fetuses with complications
- Presence of an underlying medical illness such as hypertension, diabetes, lupus, disorder of the thyroid gland, heart disease or kidney disease
- Post term pregnancy or your pregnancy has reached two weeks beyond your due date
- You have a history of loss of pregnancy
- Fetus has decreased movements or fetal growth problems are determined
- Presence of increased amniotic fluid or decreased amniotic fluid
- Rh sensitization, a condition characterized by presence of Rh negative blood group in mother and Rh positive blood group in the baby
- Abnormal results of other prenatal tests
You might be recommended by your physician to undergo nonstress test either once or two times per week. In occasional cases, you may be required to undergo it daily depending upon your and your baby’s health. For instance, you might be recommended to undergo regular non stress test if it is suspected that your baby is not getting sufficient amount of oxygen. You might have to undergo a repeat non stress test if your baby had shown negative health changes during the previous test.
Are There Any Risks of Nonstress Test?
There are no physical risks to either you or your baby associated with a nonstress test, which a noninvasive prenatal test. However, undergoing nonstress test may become a cause of anxiety in pregnant females. False positive results may also occur where a problem is detected when there is none. Moreover, it may not be able to detect a problem that actually exists.
Also, you should be aware of the fact that nonstress is a frequently recommended test for females with an increased risk of loss of pregnancy; however, whether the test is actually helpful or not is not always clear.
How Is a Nonstress Test Done?
Nonstress test is usually recommended after 28 weeks of pregnancy because before that the fetus is immature and cannot respond to the test. The test is usually performed in a doctor’s office.
During the test: You will be asked to lie on a reclining bed. Your blood pressure will be monitored before and throughout the test. Your physician will place two belts that have monitors attached to them on your abdominal area. One belt is to record the heart rate of your baby and the other is to record any uterine contractions that may develop. You would be told to press a button while you notice a movement of your baby. The movement of your baby will be recorded on the fetal heart record. Your physician will monitor whether your baby’s heart beat increases when she moves.
Duration: The normal duration of a nonstress test is about 20 minutes; however, if your baby is sleeping, then you may to undergo testing for an extended amount of time of 20 minutes. This is done with an expectation that your baby will wake up and the results obtained are accurate. Your physician may try to wake your baby up by making a loud noise or by offering you a glass of juice.
After the test: After the test, your physician will discuss the results.
How to Interpret the Test Results?
Normal–Reactive
The result is considered normal (or reactive) when the heartbeat of your baby during movement is faster by at least 15 beats per minute of her resting rate for duration of at least 15 seconds on two different times during the test of 20 minutes. A normal test implies that on this occasion your baby is doing fine and you may be asked to undergo repeat testing every week till the time of delivery.
Abnormal–Nonreactive
The result is considered nonreactive if your baby’s heart beat does not increase with movement or your baby is not moving after 90 minutes. A nonreactive test does not necessarily imply that your baby is not fine. It just implies that the test was unsuccessful to provide enough information and you would have to undergo either NST again or other tests including the contraction stress test or the biophysical profile.
However, in cases the physician feels that your baby is not getting enough oxygen, they may decide to deliver the baby.
Why Does the Test Measure Uterine Contractions?
The test measures uterine contractions because by this stage you may be developing Braxton-Hicks contractions. These are usually mild, occur sporadically and irregular. However, if your pregnancy is less than 37 weeks and you are having uterine contractions that are continuous, and occurs repetitively and regularly, then you may be going for preterm labor. Your physician may check your cervix for the presence of dilatation.
The uterine contractions are also measured during NST to check if the heart rate of your baby decreases while you are having them, which implies that some problem exists in your placenta and your baby is not getting enough oxygen.
Watch a video to learn how a nonstress test is like in real life: