Maternity - Pregnancy, part 6: Diagnostics: Nonstress Test, Biophysical Profile, Contraction Stress Test
September 08, 2021 Updated: November 29, 2021 7 min read
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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