Maternity - Pregnancy, part 6: Diagnostics: Nonstress Test, Biophysical Profile, Contraction Stress Test
by Meris Shuwarger BSN, RN, CEN, TCRN September 08, 2021 Updated: August 09, 2023 5 min read
In this video and article, we cover three important diagnostic exams during pregnancy: a nonstress test, a biophysical profile, and a contraction stress test. These tests help us understand the health of the baby.
This series follows along with our Maternity Nursing Flashcards which are intended to help RN and PN nursing students study for nursing school exams, including the ATI, HESI, and NCLEX.
A nonstress test is a non-invasive test done in the third trimester of pregnancy to measure the fetal heart rate response to fetal movement. A nonstress test may be indicated when there is decreased fetal movement, advanced maternal age, gestational hypertension, or postmaturity (post-42 weeks gestation).
A nonstress test gets its name because it does not put the patient or the baby under any stress to perform the procedure, it's just monitoring what the baby is doing.
A nonstress test usually involves two devices: a tocometer and a Doppler. A tocometer measures the stress that the uterus is under, like whether or not it's contracting. And then the Doppler is a fetal heart rate ultrasound transducer.
Patient teaching for the nonstress test is that the patient will push a button when they feel fetal movement. As Meris notes in the video, this button is not always available, but if it is, that's its purpose — to indicate when exactly the patient felt fetal movement.
If the fetus is sleeping, a vibroacoustic device may be used to awaken them. A vibroacoustic device is placed on the patient's abdomen near where the fetal head is, and sound is emitted for several seconds. Theoretically, this wakes the baby up.
Results in a nonstress test can be either reactive or nonreactive. The desired result of an NST is an acceleration — the baby's heart rate should increase or accelerate while they are moving around.
Reactive results on a nonstress test are considered normal, and indicate that the fetal heart rate is a normal rate, with moderate variability, and accelerates by greater than 15 beats per minute for greater than 15 seconds, more than twice, within 20 minutes.
A nonreactive result on a nonstress test is abnormal and occurs when fetal heart rate does not accelerate sufficiently with fetal movement. Further testing after a nonreactive nonstress test is recommended. Usually the tests that would follow a nonreactive nonstress test is a biophysical profile or a contraction stress test.
It's important to note that a nonreactive nonstress test result does not indicate anything bad in and of itself, just that the heart rate is not accelerating as expected, and more tests should be done to investigate. As Meris shares at the end of the video, her daughter "failed" almost every NST but was born perfectly healthy.
A biophysical profile is a non-invasive assessment of fetal well-being using ultrasound and a nonstress test. There are multiple components to a biophysical profile, described below. The following components make up the biophysical profile and each of them is scored with 0 points or 2 points.
In a biophysical profile, an overall score of 8-10 is considered normal, where less than 8 is considered indicative of fetal hypoxia, which means the baby might not be getting enough oxygen, and labor may need to be induced.
Fetal heart rate/NST (0-2 points)
The first component of a biophysical profile is a fetal heart rate test, usually a nonstress test as described above. A nonstress test may be done on its own, or it may become part of the overall biophysical profile if more tests are done after. A reactive result to a nonstress test results in a score of 2, non-reactive is 0.
Fetal breathing movements (0-2 points)
Fetal breathing movements can be measured as part of a biophysical profile. Is the baby making movements of breathing? This is something that babies do in utero to practice breathing so that they can transfer from the uterus to the outside world healthily.
Fetal breathing movements happening one or more times for 30 seconds is a score of 2, while absent breathing movements or breathing movements under 30 seconds are a score of 0.
Gross body movements (0-2 points)
Gross body movements measure the amount of fetal body movement. Is the baby moving their body or their limbs?
Three or more body/limb movements is a score of 2, while less than 3 movements in the same time frame is a score of 0.
Fetal tone (0-2 points)
Fetal tone is a measure extension in flexion of the head and neck. One or more episode of extension and flexion is considered a score of 2, while no or slow movement is a score of 0.
Amniotic fluid volume (0-2 points)
Amniotic fluid volume is, like it sounds, a measure of amniotic fluid — measured in pockets around the baby. If there is at least one pocket of fluid 2 or more centimeters, that is a score of 2. Less than one pocket of this size would result in a score of 0.
Contraction stress test
A contraction stress test is an invasive test to stress the baby and measure fetal heart rate response to an induced contraction. A contraction stress test may be indicated for high-risk pregnancies or after a nonreactive nonstress test result.
As Meris notes in the video, contraction stress tests are not as common as they once were in the US, given the advancements in ultrasound technology.
In a contraction stress test, contractions need to be induced. Hopefully the contractions are not enough to induce labor, but just enough to stress the baby and have them respond. There are several ways to induce contractions involving oxytocin.
Oxytocin can be produced by the body in response to nipple stimulation (oxytocin is released during breastfeeding). So, the patient may need teaching how to stimulate their own nipples to try to release oxytocin to cause a contraction. Check out our Med-Surg flashcards for an Endocrine system review, including the hormone oxytocin.
Again, a contraction stress test checks for whether or not the fetal heart rate decelerates late (e.g., it doesn't return to normal by the time it should have). Thus, a negative result is normal.
A negative (normal) result would be three contractions in 10 minutes with no late decelerations of fetal heart rate.
A positive (abnormal) result would be marked by late decelerations in at least 50% of contractions. This result may indicate uteroplacental insufficiency, which is decreased blood flow coming to the baby, which can lead to fetal hypoxia.
Stimulating a contraction can get the ball rolling and lead to labor! For your patient, this could mean an induction of preterm labor. Thus, a contraction stress test should always be performed in a hospital setting where they are prepared to deliver a baby or further assist the patient with complications involved in induction of preterm labor.
Hi, I'm Meris, and in this video, I'm going to be talking to you about some different diagnostic procedures that can be performed in pregnancy. We're going to be talking about nonstress tests, biophysical profiles, and contraction stress tests. If you stay to the end, I will tell you a little bit about my experience with an NST and a BPP. All right. Let's get started.
Okay. So first up, we're going to talk about a nonstress test.
Let's just talk about the name first. Nonstress, this means that we are not actually putting the baby or the mother under any stress to perform this procedure. This is just us monitoring what is happening with the baby inside mom. That is all. So we're not stressing any of them out. We're just watching. We're just monitoring.
So a nonstress test means that we are going to put two things on the mom, in most cases. You can have a tocometer which is going to measure the stress that the uterus is under, like is it contracting at all or not? And then you'll have the fetal heart rate ultrasound transducer or the Doppler. It can also be done just with the Doppler itself. It just kind of depends on what the provider's setup looks like.
In most cases, mom will also be given a button to push, and that button should be pushed whenever the baby moves and mom feels it. Again, not always the case. I personally have had a lot of NSTs, and sometimes, I was given the button to push. Sometimes, I wasn't. But if you ever should see that, then that's-- the purpose of the button is, "I felt the baby move. I'm pushing the button," and it's going to put a little mark on the fetal heart rate strip to say, "At this moment, mom felt movement."
What are we looking for? So an NST can either be called reactive or non-reactive.
We want it to be reactive. So what we want to see is something called an acceleration. We want the baby's heart rate to increase, to accelerate, by 15 beats a minute for at least 15 seconds in duration, two times during the NST, which is going to be for 20 minutes. So let's say that again.
The NST itself, that test is going to last for 20 minutes, and in that time, we want to see baby's heart rate go up by 15 beats a minute and stay elevated for at least 15 seconds, two times. That would be called reactive, and that means that it looks like baby is getting enough oxygen and things are going well.
Now, if we have a non-reactive NST, that means that the fetal heart rate is not accelerating sufficiently, and this means that we need more testing.
A non-reactive NST doesn't mean anything by itself. It just gives us this first thing that says, "Nope, we didn't pass this test. Let's move on."
So the NST can be done for a lot of reasons. It can be done, for instance, if a patient says, "I haven't felt my baby move today." We could do that. It may be done routinely.
This could be done because a patient is of advanced maternal age.
Maybe they have a history of pregnancy complications.
Maybe they're post-date, meaning they have gone past their due date. There's a lot of different reasons that it could happen, but the point is we're checking in on the well-being of baby and their ability to properly oxygenate.
Now, let's say we failed that test. It was non-reactive. We will probably move on to something called a biophysical profile, a BPP. In a BPP, you'll see here that we have this nice table for you to kind of spell out what goes into a BPP. A BPP-- sorry, it's hard to keep saying that over and over. This is going to be using the NST and ultrasound to assess the baby's well-being. So we have five categories here.
We have the fetal heart rate based on NST. Was the NST reactive or was it non-reactive?
You'll see here, too, that everything gets a score of either two or zero. There are no one-point scores. Okay.
So if it was reactive, we get two points. If it was not reactive, we get zero points.
The next category is fetal breathing movements. Is the baby making movements of breathing? Which is something that they do in utero to practice breathing so that they can transfer from the uterus to extrauterine life appropriately. Do we see at least one, if not more, in 30 seconds? Great. Two points. None? Then no points.
Gross body movements, so if we see baby moving their body, then they're going to get two points. If there are greater than or equal to three body or limb movements, and if there's less than three movements, they get zero points.
Fetal tone, this has to do with extension in flexion of the head and neck. So if we do see at least one episode of extension and flexion of the head and neck, they get two points. If not, zero points.
And then amniotic fluid volume, they will actually measure the pocket of amniotic fluid around the baby. And if there is greater than or equal to one pocket, so at least one pocket that has more than two centimeters of fluid, two centimeters or more, they get both of those points. If not, then they don't.
So the big things to know, we have the fetal heart rate NST, we have gross body movements, breathing movements, the fetal attitude, the flexion and extension, and then we have the amniotic fluid as well. What do we do with this information?
Well, 8 to 10 is considered normal, so that would be reassuring, and we would say, "Okay, everything looks good."
If we have less than 8, though, that is indicative of fetal hypoxia. Baby is not getting enough oxygen, and we need to do something about this.
Typically, that's going to be bringing the baby earthside, right? We're going to deliver the baby. That may not always be the case, but that is the cutoff. A score below 8 means fetal hypoxia could be possible.
Now, if I failed my NST, I could also go on to have something called a contraction stress test, a CST. So again, look at the name, it is saying a contraction stress test.
We are stressing the baby by inducing contractions. Not inducing labor, hopefully, but just causing contractions and stressing the baby out that way. I have only seen this a handful of times since I started working in OB-GYN back in the early 2000s.
This is not something that is routinely done now that we have ultrasounds so commonly available, you could do the BPPs instead, but still important to know in case you should ever see it. So what we're going to do here? Same thing.
We're going to be putting the tocometer on and the fetal heart rate transducer, the Doppler, and we're going to be watching what happens to baby's heart rate when contractions happen.
So how do we make contractions happen? Well, we can either do nipple stimulation, teach the patient to stimulate their own nipples to try and release oxytocin to, then, cause contractions, or we can actually give oxytocin to the patient.
Now, if you remember, this oxytocin is what helps to cause labor, so we are putting our patient at risk for preterm labor.
We could go from having just a few contractions to having full-blown labor, so this is not a test that should be taken lightly. So in the case of the NST, remember that reactive or positive is good.
That is not the case here. We want to have a negative CST. So what this means is that we have three contractions in 10 minutes, but we don't see any late deceleration, and we'll talk about what those decels are in a later video. But no late decelerations in those three contractions in 10 minutes? Awesome. We love it. Baby's doing okay.
However, if we see late decels in greater than or equal to 50% of those contractions, this could indicate that the baby's not getting enough oxygen due to placental insufficiency. Very bad. We don't like that.
So quick recap:
NST, it's not stressing the baby. I want it to be positive, right, I want it to be reactive.
CST is stressing the baby. It can lead to preterm labor. It's more dangerous. I don't want it to be positive. A positive CST is a bad thing.
And then BPP is just using ultrasound, and that is going to help give us a really comprehensive picture of what's going on with the baby's oxygenation status.
I hope that review was helpful. Please be sure to like this video if it was, and if you have a great way to remember something or something that I didn't cover that you want to add, I would love to hear about it in a comment below. Thanks so much and happy studying.
Okay. So I actually had to get a nonstress test twice a week with both of my children because of my genetic condition. They just thought it wise to check in on the babies. And my daughter, she failed almost every single one. I mean, she would never be reactive, and I don't know why, she's perfectly healthy, but for some reason she just didn't want to cooperate. One time, she failed, and I had a BPP done and she scored a six and they sent me over to the hospital and I had my daughter via C-section that night.
No explanation for what was wrong with her. She was born perfectly healthy and fine, didn't spend any time in the NICU or anything like that, but my doctor said, "Sometimes, they just do better on the outside," and so it was time for her to come that time, I guess. But my son, though, was a rock star and passed every single NST, and it was fantastic. So thank you, Finley, for being an NST rock star.
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