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A Visual Tour of an Non-Stress Test

While there are many sites that explain what a non-stress test (NST) is, it isn’t often we get to see what they look like.

Here, I will describe what we are seeing, playing tour guide around a strapped belly that kindly allows us a vantage point.

There are two colors of the elastic straps; the color is inconsequential, a random choice as to which monitor it goes on. As you can see, the colors, pink and blue, are deliciously sexist. 

The pink strap here is holding the fetal heart monitor on the mom’s belly. The elastic has slits in it so the band can be adjusted, tightly, around mom’s stomach, holding the monitor in place. Women need to sit still with the monitor on lest it wiggle out of listening zone on the baby’s upper back (where the heartbeat is heard clearest). Laughing, turning from one side to the other, lying back or sitting up more can all require a re-adjustment of both monitors. You can see why, in the middle of labor, it would be easier to have a mom monitored with an epidural; women without one move all over the place, requiring the nurse to adjust and re-adjust it over and over again. 

The monitor on the mom listens and the bedside machine (also called the monitor) clomps out the sound of the baby’s heartbeat as well as blinks the heart rate to one side of the machine. When the monitor is “listening” accurately, it can sound like a horse galloping down the street. Clompity clomp, clompity clomp, clompity clomp… at a clip of 120 to 160 beats per minute. Looking at the bedside monitor strip (see picture below), the baby’s heartbeat is the top squiggly line. With education and experience, a nurse/doctor/midwife is able to look at the line and determine the baby’s well-being. A line that doesn’t change much is considered “flat” and not a positive sign, especially if it stays flat during a contraction, meaning the baby isn’t reacting to the increasing pressure. We’d want to see the baby have some reaction, hopefully the heart rate going up slightly. 

While listening can be helpful, it really is easier to look at the strip, comparing the contraction to the baby’s heart rate. There are nuances that can give information about how the baby is doing during labor. When we hear (which usually comes first) a beat that’s half that fast, the first thing to do is make sure the mother’s pulse isn’t being picked up, quickly adjusting the monitor and, at the same time, feeling for the mother’s pulse on her wrist, seeing if the beats match. If they do not and the heart rate does not recover with position changes or stopping contractions, mama’s (most likely) off to have a baby in the operating room – fast. 

Here is a fabulous site that discusses the variations of normal and abnormal when looking at fetal heart tracings in labor.

The monitor under the blue strap measures uterine contractions (UCs). The technical name for monitoring a contraction is tocodynameter (I was corrected. Sorry for the initial incorrect name.). You might hear the nurse say, “Toco” and she’s talking about the transducer and its need to to be adjusted or some other reference to the monitor. 

This monitor is placed on the fundus, the top of the uterus. A nipple-like button rests between the round monitor and the mom’s skin. As a contraction comes, the button gets squeezed and measured on the bedside monitor just like the fetal heart beat one, but on its own line (the bottom line in the picture).

I turned the picture on its side so you can see the two lines. See the bottom one with the mountain? That mountain is a contraction. This mom was not on pitocin. 

Just like the fetal monitor, if mom wiggles or shifts positions, the monitor can slide down and not register any contractions if mom is having any. Or, if mom shifts in a way that the monitor is tighter, it can look, to the lay person, that the mom is having some helacious contractions when, in fact, the baseline has moved way up. Put another way, while the fetal monitor blinks out the actual heart rate of the baby (actually, it’s about 1-2 seconds behind the beats), the UC monitor “rates” the level of contractions, from 0 to about 100. If the monitor is placed correctly, the machine is “zero’d out” and the monitor's numbers dive down to the steady 20 of no contraction. As the contraction builds, the number climbs, usually slowly, over the course of about 45 seconds or so and then starts its descent, ending again at 20. Women having mild contractions might register about 45 or so whereas I have seen pitocin’d women go so high the monitor doesn’t register it and the paper has a flat line across the top until a contraction goes down again and is able to be seen on the paper.

A comment from Cindy says it in a more technical manner:

"The appearance of the contractions on the tracing is based on maternal habititus, placement of the monitor, fetal position, and lastly ctx strength. When the belt is moved, it is completely random where the ctx. tracing now prints. WIth an Intra-Uterine Pressure Catheter (IUPC) the ctx. tracing would show resting tone and strength."

If the monitor is properly placed and calibrated, going that high would, in my experience, prompt the nurse to cut the pitocin off so mom’s uterus doesn’t explode or the baby doesn’t suffocate from the intensity of the squeezing of the uterus. 

Look again at the picture above. Look on the left page and see how the bottom line is very close to the bottom of the paper? That’s pretty zero’d out. Then, after the contraction, see how much higher the line is? Mom must have moved and shifted the “zero” on the monitor. So, if she had another contraction with that higher baseline, it can look like she’s having a much bigger contraction when it really was about the same as the one before. If people don’t know about the zero-ing the machine out, they could think, erroneously, that the contraction is “a huge one!” when, in fact, the gauge began at 70 and the UC was quite mild. 

Hey, here’s an idea for the family and support people. Instead of watching the monitor for all these numbers, how about we watch and be with the mother! She will tell you, accurately (if she doesn’t have an epidural, of course), what the contraction is doing. She can feel it going up, topping out and then going down. Isn’t that amazing?! I always think contractions are so incredible… that our bodies have the wherewithal to propel a baby out of the host body. It boggles the mind sometimes. 

Now, look at the top picture again. See the thingie the mom is holding with a button on the end? This is a marker for mom to press when the baby moves. This puts a hash mark on the bedside monitor’s paper so the person reading the strip can see how the baby does with fetal movement. Little tiny arrows point, next to the upper/fetal heart rate line to make it easier to read. Experienced nurses sometimes forego the button pushing because, with practice, it is possible to see the baby’s movements with the heart rate shiftings. 

So, there’s your tour of the image of a Non-Stress Test. This, of course, doesn’t speak to the need of an NST or how to prepare for one, but this is a start. Hope you enjoyed yourself!



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Reader Comments (27)

while this is super fascinating, i really hope i never need one of those, it looks horribly boring and uncomfortable. and its really strange to me that doctors are always talking about how not to lay on your back and that doppler needs to be limited, but i have heard of these nst's lasting well into hours and being done once a day for up to a week or two, sometimes without there being any indication other than being past due.

i would love to hear your stance on how beneficial the info of an nst is and if there are other ways to gain this information that may be less stressful on mom and baby.

January 16, 2010 | Unregistered Commenterdanielle

The typical NST for post-dates schedule is every 3 days. My client right now is having BP issues and is on the every 3 day schedule.

It can be boring sitting there for a couple of hours. A productive NST can be done in 20 minutes, but it usually is about an hour. Only when it is a non-reactive strip or the baby looks like s/he's having a hard time, then it can be longer. Women sit in a reclining position, not on their backs; sometimes on their sides.

I ask my clients to do q 3 days BPP once they are past 41 wks; I learned that a BPP is actually more indicative of well-being than an NST. I have an independent sonographer who is wildly accurate and very, very kind to my clients. I'm not worried the hospital won't let my client out of their grasp, either since the BPP doesn't happen in the hospital or a doctor's office.

If I didn't think I would get more information from the BPP (or NST), I wouldn't ask for them.

Did I answer your questions?

January 16, 2010 | Registered CommenterNavelgazing Midwife

There are several mis-statements in your article. First of all, the belt that monitors the contractions is not a "tocolysis". It is a tocodynameter. Tocolysis is the process of stopping ctxs as in pre-term labor.

With an external contraction monitor, the numbers on the EFM tracing don't mean anything. The appearance of the contractions on the tracing is based on maternal habititus, placement of the monitor, fetal position, and lastly ctx strength. When the belt is moved, it is completely random where the ctx. tracing now prints. WIth an Intra-Uterine Pressure Catheter (IUPC) the ctx. tracing would show resting tone and strength.

Hope this helps clarify things.

January 16, 2010 | Unregistered CommenterCindy

Also, a BPP is going to give you more info then a NST because it gathers more info. In addition to the NST, it also measure fetal tone, breathing, movement, and Amniotic Fluid Index (AFI) A NST still is obtained so that could take more than 20 minutes if the strip isn't reactive in that time. A Reactive NST would be if 3 accels of 15 beats by 15 beats were present in 20 minutes. It may take more than 20 minutes to get a Reactive test if it appears that the fetus is sleeping.

January 16, 2010 | Unregistered CommenterCindy

Thanks! I'll correct the points this evening.

All in all, not bad for a woman who's never gone to an NST class. :) But, you are right... the information needs to be correct. Thank you.

January 16, 2010 | Registered CommenterNavelgazing Midwife

Very interesting and informative article! From the viewpoint of someone who's not yet pregnant and has thus never gone through childbirth, I keep going back to one thought - I could NOT do that. I couldn't imagine being forced to labor with straps around my belly and a "task" (pushing the button), stretched out on my back. Even though I've not yet been through the experience, I know myself well enough to be sure that I could never go through labor that way. It seems bizarre and unnatural and uncomfortable - how can a woman focus on what she needs to do - how can she listen to her body and her baby's - how can she trust in herself - with so much exterior interference?

January 16, 2010 | Unregistered CommenterKate

Ah, but Kate... be *very* careful what you say about "never." There are valid reasons for doing ALL "interventions" that are offered/done in hospitals. Their indiscriminate use is abhorrant; their judicious use can be life-saving.

And the NST is not done during labor. The strip I shared was from a labor, but that was just demo purposes. Women typically have no contractions during an NST. It's just sitting and being bored for awhile.

But, you are right. Those *are* the monitors used when women are in labor and yes, they do have to sit still or they go wonkie and the nurses get cranky adjusting them over and over.

I just really want to caution you about saying you will not do something. The Universe will smack you hard with a "Oh, yeah? Watch this!"

January 16, 2010 | Registered CommenterNavelgazing Midwife

I remember telling my midwife, sometime in the 8th month when we were discussing birth plan type stuff, "I just don't want to labor hooked up to all kinds of wires." And she said, "We'll do everything we can so that you don't have to, but sometimes things happen."

Indeed they do. That's exactly how I ended up laboring.

I didn't have an epidural, and indeed the nurses really get cranky when you move around. They're in other rooms with other patients, and they see the heart rate dipping on the monitor and they rush in, only to find out the problem is the sensor isn't in the right place anymore.

I was extremely fortunate that, when necessary, the midwife and the nurse (shift change, new nurse, awesome nurse) took turns holding it in place and moving it as necessary. They also let me unhook from the monitors to go to the bathroom, and didn't harass me when I lingered there a bit longer than absolutely necessary.

I am under no illusion that I got standard hospital treatment, and I often wonder if I would have ended up with a C-section for fetal distress with a different set of attendants.

January 16, 2010 | Unregistered Commenterchingona

Oh, and it is unnatural and kind of uncomfortable, and it is hard to not to get distracted by the monitors. But you just do what you need to do.

January 16, 2010 | Unregistered Commenterchingona

Chingona: I, too, spend a lot of time holding the monitor on my clients so they can move around. I also have no fear about moving it to be able to find the baby. After permission from the nurse, I also remove the leads from the machine, wrap them around mom's neck and off she goes to the bathroom.

It sounds like you had wonderful support. I'm glad.

January 17, 2010 | Registered CommenterNavelgazing Midwife

Just to clarify again, you cannot tell the strength of the contractions from how high the tracing is with an external contraction monitor (toco). The toco accurately measures how often a contraction occurs and how long it lasts, but does not accurately measure intensity. The way to measure intensity of a contraction with a toco on is to feel the mom's belly during a contraction.

The IUPC (intrauterine pressure catheter) is the only thing that will accurately measure the intensity of a contraction. When you are using an IUPC, the readout on the tracing is an accurate picture of contraction strength.

Also - you're right in that an NST is not used during labor (at that point, it would be a CST or contraction stress test). However, if continuous monitoring is indicated and you have a CNM who actually labor sits (like me!), it's not a problem to get out of bed. I'm there the entire time and have no problem readjusting the monitors as needed. Most of the time though, our women just have intermittent monitoring and don't have to deal with the straps or restrictions on their movements!

January 17, 2010 | Unregistered CommenterEmily

I posted late last night and didn't give it as much thought as I should have; thanks for calling me on that.

I'd just like to clarify that I'm not anti-modern medicine, anti-doctor or anti-necessary intervention. I AM, however, anti-overmedicalization. I'm very, very grateful that we live in a civilization where heroic and lifesaving procedures are available for mothers and babies who need them, but I'm also a staunch opponent (regarding myself personally - not judging anyone else) of convenience c-sections, "preventative" medicine for immensely improbable scenarios, and unnecessary intervention. From a spiritual/philosophical point of view, I have a difficult time reconciling that our bodies are evolved to safely and efficiently bear children, but our society and mainstream medicine have minimized that fact in favor of perpetuating ignorance and misinformation in the name of false perception of safety and convenience.

I'm sorry if my comment above made it seem like I'm not in favor of lifesaving and/or truly necessary procedures. I'm glad that those opportunities exist and an be rapidly utilized when necessary; I just believe that Big Insurance and ignorant (in the denotative sense) OBs have a very skewed idea of "necessary." Which is also why I'm so appreciative of your blog and the educational opportunities it offers, as well as of the midwifery practice in general, and the rare breed of OBs that truly do understand every aspect of the birth process.

Anyway, that's what I get for posting when I'm half asleep! :-P Thank you for the opportunity to (attempt to) clear things up a bit.

January 17, 2010 | Unregistered CommenterKate

I totally appreciate the added information, Kate.

What's interesting about the our-bodies-are-perfect-and-when-left-alone-will-deliver-just-fine concept is it doesn't take into account our present lifestyles.

Recliners that create persistant posterior labors, horrid diets that make for fat women, PCOS/Insulin Resistance that hinders the uterus' ability to function properly (fat women have a LOT of failure to progress situations), crap food doesn't give the body what it needs to be as strong as it could, no/little exercise that softens the woman, possibly causing her to feel more pain than her ancient sisters who *knew* pain, lack of Vitamin D that can hinder the uterus' contractibility... and then there's the way we labor... in a bed that doesn't allow the "dance" of mom and baby so babies can get stuck in the wrong position, AROM that drops acynclitic babies into the pelvis where they get stuck, epidurals that anesthetize women and affect labors (no matter what the research keeps showing)... and we could go on and on.

Laboring/Birthing just isn't what it used to be. Even 150 years ago. So, in this light, our bodies, for birth, are not given the CHANCE to be normal.

January 17, 2010 | Registered CommenterNavelgazing Midwife


I pretty much agree with you on all of that. I am anti-overmedicalization, anti-unnecessary intervention, anti-convenience C-section, anti-ignorance. But it's not like only women who want to be on continuous monitoring end up with continuous monitoring. I didn't go in begging for an induction and saying "Hook me up to the monitor!" Obviously, I have no idea what would have happened if I had declined the induction and forced my way out of that hospital. Maybe things would have been fine. But before I went in for the NST, I had two days with no fetal movement. I LISTENED to my body and my baby, and they said something is not right here.

And then once you're in that situation, you can't just throw up your hands and say "Oh, I couldn't possibly." The baby has to come out, and if I had just given up and pouted that the monitors prevented me from laboring and moving and listening to my body, I certainly would have ended up with a C-section. So I labored with monitors and wires.

When you believe too strongly that "our bodies are designed to do this" and something happens that requires or indicates an intervention, you end up feeling like shit because you think your body "failed." Just ... be careful about what you set yourself up for and be careful what assumptions you make about women that have different experiences.

I was a lot more absolutist about these things before I had a complication arise. I'm pregnant again, and I'm doing everything I can to avoid a hospital birth, just like I did the first time, but ... shit happens.

January 17, 2010 | Unregistered Commenterchingona

Let me put this another way, Kate. A less testy way.

When I was getting set up for the induction, I was really upset, and I was crying. And some of the hospital nurses were being openly contemptuous of me for even caring one way or the other. My midwife said to me that I had every right to be upset, that this was going to be a lot more difficult than a natural labor, that I should go ahead and cry and let it out. But ... once I'd done that, I needed to get myself in a zen-type position where I could be okay with whatever happened because staying hung up on it wouldn't help me get through it and would probably make it harder.

That was really good advice, and that's what I'm trying to get at.

January 17, 2010 | Unregistered Commenterchingona

Barb - is that CTG trace taken from one of your own clients - it looks like it was v v sleepy/unreactive with poor beat-to-beat for a loooooong time judging by the folds in the paper...?? The variability looks crap & there are no accelerations with the contraction - was it pathological?

January 17, 2010 | Unregistered CommenterLiz

Yes, a client. She was 8cm, but there for several hours. About 3 hours after this pic, a beautiful, healthy girl was born via cesarean.

I *love* discussing strips.

January 17, 2010 | Registered CommenterNavelgazing Midwife

Eh, that tracing doesn't look so bad to me. We can only see 6-7 minutes of it, and in that, I don't see anything particularly concerning. The variabilty looks average to me (6-25 bpm is "average") and there are no decels. Looks like a sleep cycle to me, without being able to see anymore than a few minutes of it.
We generally use intermittent monitoring at my hospital unless the laboring client has reason to switch to continuous. (Reasons include any pregnancy complication, concern about the fetus, and also pain medicine or pitocin) We tell our clients that their job is to get comfortable, and our it's our job to worry about the monitor. It can be harder to monitor as mom moves, but it's not impossible.

January 17, 2010 | Unregistered Commenterdoctorjen

Exhibit A showing how subjective reading a strip can be.

Thanks, DoctorJen... as always.

January 17, 2010 | Registered CommenterNavelgazing Midwife

I had the monitor on in my first and second labours. It was hospital policy. For #1 I didn't notice the monitor, I was already in transition when I arrived. With #2 I loved the sound of the monitor- I was completely alone in the dark and the sound was so soothing and almost put me to sleep. For #3 I was only monitored by the doppler (same hospital but different antenatal care program). #4 is due in 9 weeks and will be a home birth.

In Australia I have only ever seen brown straps used (3 hospitals and 2 different states).

January 18, 2010 | Unregistered CommenterMarie

I should have remembered - that is an American trace - you use different paper to us. To me it looked like a pretty horrible 45 minute trace!!

January 19, 2010 | Unregistered CommenterLiz

Women having mild contractions might register about 45 or so whereas I have seen pitocin’d women go so high the monitor doesn’t register it and the paper has a flat line across the top until a contraction goes down again and is able to be seen on the paper.

Yes, agree with other posters, with external monitor the number itself means nothing. only with an internal contraction monitor would the 45 or flat line across the top give any useful info.

January 19, 2010 | Unregistered CommenterDenise

I never had a NST, I was supposed to schedule one towards the end of my 40th week and went into labor before then. Are there certain times during a labor when traces are done? I.e. is it usual to want to get a trace prior to pushing? I went through transition in the tub and when I no longer wanted to be in the tub and needed to push, they said they had to do a trace on me. In my case, they wanted me to get out of the tub and walk over to the bed for monitoring and a vaginal exam and I did NOT want to move.

Turns out baby's head was visible and palpable once my nurse checked (I had told her, "Baby now!" before she checked and had warned her that I expected the second stage of labor to be quick). I ended up having the baby less than five minutes later in the tub, the resident's first tub birth, apparently. They never did get that trace on me...

January 20, 2010 | Unregistered CommenterJen

Jen: The NST is different than a strip in labor. They often want at least one 20-min. strip in labor to prove, in court, that you were monitored. Of course they *do* want to see what's happening with the baby, too, but it doesn't sound what they were looking for with you.

Great birth, it sounds like. Congrats!

January 20, 2010 | Registered CommenterNavelgazing Midwife

I've done this fun game twice. The first time in labour with DS when I didn't have the foggiest what was going on. The second time last Tuesday, because baby's heart rate was high. (trace showed everything normal, btw :-) ) The MW was lovely and explained it all to me afterwards. While I was lay there I kept thinking, "sheesh, this is the longest half hour of my life! I can't imagine what it would be like to be stuck like this in labour.... oh no wait, I've BEEN there and it was horrible! Note to self, do not do that again."

May 21, 2010 | Unregistered CommenterSam

I'm 36 years old and in good health. My pregnancy has been uneventful, as we all hope when we get pregnant, regardless of our age. My level 2 US was normal, baby looked great...everything looked normal.

However, despite this and all other tests being normal, my doctor sent in an order for me to have NST and AFI twice a week for being AMA.

I'm not over due. I've not had any issues. Is this onslaught of testing truly necessary just because I'm 36?

I called to decline the testing, based on my history (I've had two previous, healthy babies and uneventful pregnancies) and the fact that everything has been normal with this pregnancy. However, I am still open to my doctor's opinions (even though she has said it's "routine for AMA patients."

That said, I know plenty of women older than me who haven't even heard of these tests. If they are routine, why the discrepancy among providers?

July 21, 2012 | Unregistered CommenterSunny

Sunny: I've heard of both scenarios... it depends on the conservativeness of the doctor. You might have one that got sued for something that wasn't found later in someone's pregnancy and he's not about to have that happen again. It's hard to say what drives some docs to go overboard with technology and why others are so easy-going.

Not much help, but good luck anyway!

July 21, 2012 | Registered CommenterNavelgazing Midwife

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