Confused about Variability & Decelerations

imenid37 · Jan 14, 2007

Variability is the fluctuation of the fetal heart rate over time. Short-term variability is the beat-to-beat fluctuation of the fetal heart rate. Long-term variability is the fluctuation of the fetal heart rate over several minutes time. The presence of variability is consistent with a mature intact autonomic nervous system. Don't confuse variability with variable decelerations which are abrupt decreases in the fetal heart rate associated w/ compression of the umbilical cord. Early decelerations occur with the contraction. They are ususally associated with fetal head compression and are often a sign of descent as labour progresses and the head descends OR if seen in early labour, they can mean cephalo-pelvic disproportion, ie. a big head which may not fit through the pelvis. Early decels in late labour are not bad, the head must be compressed in order for the baby to be born. The patient should be checked if you start to see persistent early decels, she may be progressing rapidly. Late decelerations begin during a contraction and persist after the contraction has ended. They are, epsecially if persistent, a sign of fetal intolerance of the labour and necessitate intervention. This is just a snippet of information. Try the books Pocket Guide to Electronic Fetal monitoring by Susuan Tucker or AWHONN's Principles and Practice of Electronic Fetal Monitoring for more complete info. Here's a website:http://www.brooksidepress.org/Products/Military_OBGYN/Textbook/LaborandDelivery/electronic_fetal_heart_monitoring.htm

luv2shopp85 · Jan 14, 2007

Thanks for your help. I really don't have money to be spending on a book though. I found a few websites that I've been reading and htey are helping a little bit.

I'm a lil confused though... isn't variability the same thing as accelerations when shown on a fetal heart rate strip? How do you tell the difference between the 2 on the strip ?

And also... with early decelerations... don't they occur right before a contractiion? Well in this picture it loooks like they are occuring at the same time or after the contraction. http://www.brooksidepress.org/Products/Military_OBGYN/Textbook/LaborandDelivery/EFM/Early.jpg Can someone elaborate on this please?

Does a contraction start as soon as the line leaves the baseline? And when it starts to get round .. is that the peak?

babyktchr, BSN, RN · Jan 14, 2007

Thanks for your help. I really don't have money to be spending on a book though. I found a few websites that I've been reading and htey are helping a little bit.
I'm a lil confused though... isn't variability the same thing as accelerations when shown on a fetal heart rate strip? How do you tell the difference between the 2 on the strip ?
And also... with early decelerations... don't they occur right before a contractiion? Well in this picture it loooks like they are occuring at the same time or after the contraction. http://www.brooksidepress.org/Products/Military_OBGYN/Textbook/LaborandDelivery/EFM/Early.jpg Can someone elaborate on this please?
Does a contraction start as soon as the line leaves the baseline? And when it starts to get round .. is that the peak?

Ok...variablility. If you think of a ECG...and the QRS complex. The spike going upwards is the "R" wave. What a fetal monitor does is place a DOT on paper that represents the fetal R wave. It continues to record dots reflecting the R wave and then the monitor draws a line to connect them. This is variability. Beat to beat fluctuations. New NICHD terms have combined short term and long term variablity, so only LTV is documented now. Accelerations are ABRUPT increases from the baseline and can be associated with or without contractions. Reactive accels are 15X15 beats (meaning they go UP for 15 seconds and then last for 15 seconds). Variability is what you interpret in BASELINE. Decelerations and accelerations are not to be considered in baseline interpretation. So, to answer your question, accels and variablity are NOT the same.

Early decels are associated with head compression and are gradual (30>seconds) decreases in baseline. This is a vagal response to head compression and usually start with contraction and end with contraction. Same criteria with lates. They are gradual from onset and occur after the peak of the contraction. Lates are reflexive, meaning, that the placenta is reacting to lack of oxygen either from decreased blood flow or some sort of placental problem (IUGR or abruption). The late onset of this decel is because of a 'lag' in time in circulation of blood to the placenta to the receptors in the fetus (chemoreceptors). The baseline returns after the contraction has already ended. Over time, lates can certainly hack away at the fetus' ability to recover, and may lead to hypoxia. You want to fix those as quickly as possible.

Variables are cord problems. They are in direct response to cord vein or artery squish, sometimes both. When the cord is squished, the fetus notices changes in pressure (baroreceptor) and speeds up heart rate to compensate for loss of perfusion (this is vein squish) . If arteries become squished, then the fetus acknowledges this change thru baro and chemo receptors, and slows the HR down to conserve oxygen. When the contraction begins to subside, the HR speeds up as oxygen is restored and returns to baseline. You don't always have the pre-variable accel. Sometimes you have just complete cord squish right away. Variables are ABRUPT decels from baseline (

This is also autonomic nervous system at work. Sympathethic and parasympathetic nervous systems need to be intact for this to work. If there are delays in maturity, or drugs on board, or fetal abnormality....all of these things can be affected.

It is a lot to absorb. I love the physiology of FHR. You can speak forever on it, and never get enough (at least for me). I hope this has helped you some.

charebec65 · Jan 15, 2007

Great responses! I'm transitioning LPN to RN and will be getting to that again at some point. I found it fascinating myself while in PN school and doing the L&D clinicals. I loved L&D.

enfermeraSG · Jan 16, 2007

If you look at the top of the OB/GYN forum this subject is a "sticky", the websites are great! Don't feel too much pressure to be able to read strips like a pro, it is a long learning process and can be tricky. I wouldn't feel like you need to "get it" as a student when it takes the floor nurses awhile to get it when we are new! Get a handle on the basics of it, make a cheatsheet if it helps. SG

Elvish, BSN, DNP, RN, NP · Jan 16, 2007

If you are doing an NST on an antepartum less than 30wks, the OBs will probably be happy with a 10x10 accel. NICHD guidelines state that this is acceptable for under 30wks. Just my .02.

babyktchr, BSN, RN · Jan 17, 2007

If you are doing an NST on an antepartum less than 30wks, the OBs will probably be happy with a 10x10 accel. NICHD guidelines state that this is acceptable for under 30wks. Just my .02.

Very true..but if this 30 weeker (or below) gives you a 15x15 accel, then this baby must be held to this standard for any subsequent antepartal testing. For those who don't archive, document document document.

Elvish, BSN, DNP, RN, NP · Jan 17, 2007

Very true..but if this 30 weeker (or below) gives you a 15x15 accel, then this baby must be held to this standard for any subsequent antepartal testing. For those who don't archive, document document document.

Good to know!

jennf83 · May 24, 2010

In a previous post, they said not to confuse variability with variable decels, how do you distinguish between them then?

dcav · May 25, 2010

I get the variability vs variable decel concept. But I'm still confused about what category a tracing that has moderate variability with non-recurrent late or variables is. If they're recurrent they're Category II. I'm thinking that the non-recurrent ones are Category II as well.

Also, I thought the term "reactive" was only applicable to NST's, but we have to document whether all tracings are reactive or non-reactive.

jennf83 · May 25, 2010

Can you explain the variability vs variable deceleration to me, because sometimes what I would think would be a variable, someone said its just variability.