It isn’t uncommon in the course of my shift for me to be sitting at the computer, happily charting away, when a well-intentioned family member/friend/visitor of a laboring mom bellies up to the counter, locks eyes with the big-screen fetal heart monitor, and starts asking questions.
Now, fetal heart monitoring is much more complicated than what I can explain in the span of this blog. There is introductory (basic) FHM, which, once passed, is one of the factors that allows a newly minted L&D nurse to work independently. Then there is intermediate FHM, which is a follow-up course that goes into more detail and depth on how to read, interpret and respond to the information we gather from our laboring moms and babies.
So what’s the big deal with fetal heart monitoring? Pretty easy: when you walk into a room and see a laboring mother, you see one patient. I see two (at least, assuming this isn’t a multiple birth!). However, of those two patients, there is one patient that I cannot directly assess because that patient is inside the other patient! So why do I watch the monitor like a hawk? Because the information on that monitor is my only direct look into how patient #2 is doing.
Let’s get into some basics. A fetal heart strip is divided into two parts: the top part is the fetal heart rate itself. This is represented by a line that moves vertically across the page to represent the baby’s heart rate in beats per minute (bpm). The bottom part is tracing the mother’s contractions.
Now, in a normal term pregnancy, I expect to see a certain amount of variability in the fetal heart rate, or the “bounce” present in the FHR. Variability is determined by looking at the fetal heart rate pattern between contractions and is a result of the fetus’s immature sympathetic and parasympathetic (vying nervous systems) pulling on each other like a tug-of-war. Sympathetic nervous system gets the upper hand and you have an increase in FHR. Parasympathetic nervous system gets the upper hand and you have a decrease in FHR. Pretty easy, right?
The FHR in the first example above tells me that baby is probably pretty darn happy in there. Especially if there are accelerations present, this typically indicates a content baby with a good placenta and good oxygen exchange.
Since what goes up must come down, there also exists a phenomenon called decelerations in fetal heart monitoring.
Early decelerations are usually a sign of head compression. When a contraction squeezes on baby and baby is getting low in the vaginal vault (and hence, close to delivery), this can trigger the baby’s vagus nerve (not Vegas, vagus!), which in turn slows the heart rate as the contraction gets stronger and squeezes harder. With this kind of deceleration, the heart rate should return to normal as the contraction lets up. L&D nurses like to see early decels because it usually means there’s a baby coming soon!
Late decelerations, on the other hand, especially if paired with minimal or absent variability, can be a sign of fetal distress. What a late deceleration tells me as an L&D nurse is that baby isn’t coping well with the stress of labor. During a contraction, blood flow to baby is temporarily suspended as the uterus contracts and cuts off the vessels leading into and out of the uterus. Normally, the blood that remains in the placenta and in baby during a contraction is oxygenated enough that a baby typically won’t notice the temporary lack of fresh O2 during a contraction. However, if baby is stressed from labor and her oxygen levels are low anyway, she may really take offense at her O2 source being cut off for any amount of time, and as a result, her heart rate drops as she’s not able to compensate. Of note: late decelerations can also be a result of an epidural, which can decrease maternal blood pressure and therefore decreases the amount of blood and O2 going to baby.
Fixes for late decelerations include: changing mom’s position to improve blood flow to the uterus, placing O2 on mom (and thus increasing the O2 going to baby), turning down/turning off Pitocin (decrease the frequency and strength of contractions so baby isn’t getting squeezed as much), turning up IV fluids (increasing the blood volume so baby is better perfused), IV ephedrine (a drug that increases maternal blood pressure if that’s the culprit) and, of course, delivery (no more contractions–yay!). If you’ve ever seen an L&D nurse (or perhaps a crowd of them) come running into a room, throw a laboring mom all over the bed and go through some variation of the steps above, you’ve probably witnessed them reacting to late decelerations.
Variable decelerations typically indicate that the umbilical cord is getting pinched. They usually happen with or around contractions. Whether baby is laying on it, squeezing it (I’ve seen it happen via ultrasound!), or the cord is around baby’s neck, body, foot, etc., if you’re seeing variable decels, usually the cord is in a wonky spot. Thankfully, variable decels aren’t usually very concerning unless they’re really deep (down into the 80-bpm or lower range) or they don’t recover fairly quickly.
Prolonged decelerations, much like late decelerations, are a sign of fetal intolerance of labor. The fixes are typically the same as those listed for late decels, though it has been my experience that especially with prolonged decels, if mom doesn’t deliver soon, she’ll probably be heading back for a C-section.
Fetal tachycardia, or a fetal heart rate with a baseline of 160bpm or greater lasting for at least 10 minutes, can be normal, especially in a particularly active baby. However, it can also be a sign of distress and indicate anything from maternal infection to fetal heart problems. I have seen tachycardic strips as a result of mom smoking a cigarette before coming into triage. I’ve also seen tachycardic strips as a result of uterine rupture and placental abruption. I’ve seen even more as a result of maternal infection (whether that be an infection of the amniotic fluid or something as normal as the flu). As a result, most L&D nurses hate, hate, hate to see strips where baby is tachy as it is usually a sign of trouble brewing.
Fetal bradycardia, while not uncommon when nearing delivery, is one of those things most L&D nurses really watch for. Unless you’re close to delivery, there is no good reason for fetal bradycardia (at least that I’ve seen!), and most fetuses that exhibit sustained bradycardia are headed for the OR if they don’t shape up!
So, now that we’ve gone through the basics, perhaps you can appreciate the following. I call it, “An Assessment of Fetal Well-Being Based on the Facial Expressions of Your Average L&D RN”.
PS: if you’re interested in further exploring the concepts in this post, please reference the following webpage, which I have found to be very thorough! Real-life FHM strips included!