Birth Matters

Electronic Fetal Monitoring

One of the biggest, if not the biggest, concerns a woman has during labor is "how is my baby doing?" Listening to the baby's heart has been used for many years to gain a sense of how the baby is tolerating labor. There are a variety of ways this can be done -- fetoscope (a modified stethoscope), handheld doppler unit, and the electronic fetal monitor (EFM). The fetoscope and hand-held doppler are used for "intermittent" monitoring -- the heart rate is measured over a short period of time (eg. through a contraction). The EFM can be used either intermittently or continuously and creates a permanent record of the baby's heart rate on paper. EFM can be done externally, by using 2 sensors, strapped to the mother's belly -- one measures uterine contractions and the other measures the heart rate via doppler. EFM can also be done internally, via a pressure catheter inserted in the uterus to detect contractions and a small electrode that is "screwed" into the baby's scalp, to detect the heart rate. Internal monitoring requires that the bag of waters or membranes are ruptured.

For women that are planning a vaginal birth after cesarean (VBAC), fetal monitoring can be a big issue. The literature shows that the most consistent indicator of a uterine rupture (a rare but extremely serious complication of VBAC) is fetal bradycardia (abnormally slow heart rate). There are other indicators of uterine rupture, these include pain, vaginal bleeding, changes in the maternal blood pressure or pulse, change in the shape of the abdomen, sudden movement of the baby back up the birth canal but fetal bradycardia is the sign that is most often seen in the hospital setting. This doesn't mean that the other signs aren't seen, but because it is relatively "easy" to monitor the baby's heart rate, many physicians require continuous fetal monitoring in the hopes of detecting a rupture quickly. There are many disadvantages to continuous EFM, and the literature has also shown that for low risk pregnancies, continuous EFM does not have any positive benefit, but does increase the number of cesareans done for "fetal distress". If a woman, after looking at all the risks and benefits to continuous EFM, consents to this type of monitoring, she needs to do everything she can to avoid the pitfalls associated with it -- and a major problem is figuring out if the baby really is distressed. Interestingly enough, ACOG (American College of Obstetricians and Gynecologists) does not formally recommend continuous monitoring during VBACs though they do state that many people think its a good idea.

How to interpret the results of monitoring, especially EFM, is a big subject. And from what I've been able to tell, true experts are pretty uncommon, and that's part of why so many babies that are taken c/s for "fetal distress" as detected by the EFM have APGARs of 9 and 10. It’s a very inexact measure of baby well-being and gives a lot of data that we really don't know how to interpret very well at all.

The first important concept is baseline heart rate. Simply put, this is the average heart rate, in beats per minute (bpm), of the baby. A "normal" baseline is between 120 and 160 bpm.

The next important concept is variability. You want the baby's heart rate to show normal variability -- it shouldn't stay right at the same rate all the time, rather, it should vary on average 5-15 bpm (beats per minute). You should see variability within the range of the normal baseline heart rate (120 - 160 bpm). A baby that shows slight or no variability is considered to be slightly in trouble, in the sense that it is indicative that s/he has no reserves. S/he is doing ok at the time but might not deal well with any other stress.

Some people are ok with a baseline heart rate that is lower or higher than "normal" as long as there is good variability. You can start to see how it gets "fuzzy" to say what's a problem and what isn't.

The next important concept is deceleration. This is when the baby's heart rate slows down, more than the normal variability. There are different types of decelerations. Some are scary, others aren't.

 

"Early decels" happen as the contraction is happening -- in other words, as the uterus squeezes, the heart rate drops and as the uterus relaxes, the heart rate goes back up.  This is due to compression on the head and usually happens during pushing (though evidently it can happen during first stage too).  It is considered a benign deceleration -- not something to be worried about.

 

"Variable decels" are just that -- variable.  They aren't usually directly associated with the contraction pattern and the amount of the deceleration is variable as well.  They don't have to be repetitive.  It's thought that they are associated with compression of the umbilical cord -- and they seem to be seen in babies that have the cord wrapped around their neck a lot of the time but often there is no obvious explanation for why variable decels are seen.  They are more often associated with ruptured membranes.  They can be made better or worse by things like vaginal exams, changing positions, sampling the baby's blood through the scalp.  If the baby has good reserves, pretty severe variable decels can be tolerated -- you'll see the heart rate go down, then speed up above baseline and then return to normal.  If the baby is already stressed (poor reserves) then the baseline itself will get higher and higher and there will be less and less variability.  That's a worrisome situation.

 

 

"Late decels" are the ones that are of the most concern.  These start at least 20 seconds into a contrctions and do pattern with the contraction -- they are repetitive. It's thought that they are caused by reduced blood flow to the uterus and hence to the baby.   They are associated with things like lying on our back, epidurals/spinals, excessively strong contractions (often pitocin, prostin or cytotec/misoprostel driven).  They can also indicate a problem like intrauterine growth retardation, hypertension, HELLP syndrome, other placental problems.  Position change may help (if the woman is lying on her back) and administration of oxygen might help.  You'll see diminished variability, a rising baseline heart rate and abnormalities in the baby's blood if they continue long enough (about 20 minutes seems to be the time frame I've seen).  The length of time it takes for the decel to resolve (come back up to baseline) is important -- if it takes a while after the contraction is over for the heart rate to come back up then that's more ominous than if it recovers with the end of the contraction.  Again, how ominous a prolonged decel is depends on the overall variability -- if variability is poor, then you have to do something if the decel looks to be lasting 3-4 minutes -- if the variability has been good, you can anticipate that even a long decel will recover well.  This is the type of decel that caregivers are looking for as an indicator of uterine rupture -- because the fundamental problem with a rupture is detachment of the placenta (a type of abruption) -- and that would result in reduced blood flow to the baby.  What little I've read about decels associated with placental abruption is that they are major -- dramatic and obvious with little or no recovery.

 

A Summary:

* Baseline Variability Reflects Fetal Reserve

* Variable Decels - Umbilical Cord Compression

* Late Decels - Placental Insufficiency

* Early Decels - Head Compression

* Decels that return slowly to baseline but don't exceed previous baseline,with normal variability and no tachycardia (heart rate above 160) don't represent asphyxia (lack of oxygen) in baby.

So, if someone comes to you saying "your baby is having decels" its important to find out which kind of decel and what kind of variability the heart rate is showing. Whether or not you try to resolve something like a variable decel or late decel would depend on how severe it was and how close you might be to the birth -- if delivery is close, most babies will do ok (if they've got those reserves). That's also part of the difficulty -- how do you really assess how much reserve the baby has?

Things that you can do to try to resolve decels:

* position change (hands and knees, lateral, knee chest)

* turn off drugs (particularly pitocin)

* amnioinfusion (pumping sterile saline back into the uterus to replace the fluids lost when the membranes were ruptured)

* give oxygen to mom

* if mom has low blood pressure, give fluids to resolve that.

 

Some of the pitfulls associated with EFM:

External EFM involves strapping 2 belts, with monitors, to the laboring woman's belly. The can be very annoying. It can be difficult to find and keep the baby's heart rate, which can then result in the woman being confined to bed or at least to one sedentary position. If the hospital doesn't have telemetry (remote) EFM units, she has to be unplugged and the re-plugged anytime she wants to leave the immediate vicinity of the monitor equipment (say, to use the bathroom). Obviously, using a shower or jacuzzi is not an option with EFM. Many woman find external EFM to be quite restrictive.

I've heard from several women that internal EFM was actually less restrictive than external EFM. The big problem with internal EFM is rupturing the membranes and all the potential problems associated with that. Artificial rupture of membranes (AROM) puts a woman "on the clock" -- most hospitals have a policy that all babies must be delivered within some arbitrary time period (range seems to be 12-24 hours) of membrane rupture, due to fears of infection. Given the frequency of vaginal exams in many hospitals, this concern may well be legitimate. Having 2 foreign objects inserted into the uterus probably makes this risk of infection even higher. AROM is associated with cord compression which shows up as decels -- you may find yourself in the situation of detecting very real distress, but distress that is the result of the monitoring itself. The thing I worry the most about with AROM is malposition -- a posterior ("sunny side up") or asynclitic (crooked head) baby -- a woman would want to be absolutely sure her baby is in an optimum position before AROM because the loss of the normal fluid cushion can make it impossible for the baby to adjust position as the labor progresses. In the case of a VBAC, many of the primary cesareans resulted because the baby was posterior, so it makes sense to be very careful about this issue. The position of the baby can be determined *before* AROM and that can be done with ultrasound if no one is experienced in manually palpating position.

 There are 3 says to confirm fetal distress:

* fetal scalp sampling: This takes a few minutes tops and really is the standard of care for confirming distress. It involves making a small cut in the baby's scalp, collecting a very small amount of blood and analyzing the blood for signs that the baby isn't getting enough oxygen.

 

 * Pulse oximetry (auk-SIM-etry): This has the advantage of being both a fetal heart monitor *and* a measure of the amount of oxygen in the blood -- it is less invasive than the screw-in electrode and will give the same information plus continuous oxygen content of the blood information -- the disadvantage is the necessity for AROM and the fact that many hospitals probably don't have it available yet for this use. But if they do, I think it might be a great option.

 

 * And lastly, evidently touching the baby's head and watching for an increase in the heart rate (the same thing they look for in a prenatal non-stress test) is a good measure of how distressed the baby really is -- if s/he is in trouble, the heart rate won't increase -- if s/he is still doing ok, the heart rate will increase and then come back to normal. But this is probably a bit too un-interventionist for most hospital situations.

Regardless of how, something should be done to confirm distress before a cesarean is done, unless the heart rate really dramatically drops. I suspect that if the decel was due to uterine rupture, it would be profound and very obvious that something really bad had just happened -- you wouldn't have to wonder if you needed to confirm it. It is the other more "run-of-the-mill" distress that needs to be confirmed.

Monitoring Fetal Heart Rate/Decels -- I've summarized a lot from this web page but you can read more about it here if you want.

Explanation of Late Decels -- another really good explanation of late decels.

I hope this has been helpful and if you are trained in this sort of monitoring and can tell me where I've misinterpreted something, please let me know!

Revised July 1, 2006