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Understanding Fetal Heart Tones: What's Normal During Labor and Delivery Monitoring?


Breathe. Relax. Drop your shoulders. You focus on each labor wave as it comes. Rock. Rest. Pressure. You are laboring hard, focusing during each moment to work with your baby to move down. You may not pay a lot of attention to the doppler routinely used to check on your baby.


Monitoring the baby's heartbeat is listening to the language of the baby and what they are telling us about their tolerance of labor. Interpreting that communication is a learned skill that is so important that the state of Texas requires a class on monitoring fetal hearttones every 2 years to keep midwives updated on their skills.


Vocabulary:

BASELINE: The most common rate of the baby's heartbeat during 10 minutes of monitoring that is occurring for at least 20% of the time.

DECELS: They are decelerations or drops in the baby's heartbeat that are at least15 bpm (beats per minute) slower than the baseline and they are lasting longer than 15 seconds.

  • Late Decels begin at the peak of a contraction or later.

  • Early Decels begin at the beginning of a contraction.

  • Variable/Random Decels are just as they sound, they don't have a pattern.

ACCELS: They are accelerations in the baby's heartbeat that are at least 15 bpm faster than the baseline and they are lasting longer than 15 seconds. It is a baby reacting to labor, movement and stimuli. It is a great sign.

VARIABILITY: A fluctuation in the the baby's heartrate of more than 5 bpm. Variability is desired and a good healthy sign.


When we assess you at the beginning of admission to the birth center or the first available time upon arrival to your home, we are establishing a baseline. This is the number that all the other numbers are based off of. We cannot tell you if a baby has accels or decels if we do not know the baseline.


The ideal heartrate pattern is a baseline of 120-160, though some mature babies may have a baseline in the 110s, with a lot of variability and accels. We want to hear that heartrate react to contractions and react to stimuli. This is the baby's way of telling us that they are doing just fine.


We are also listening to patterns in the baby's heartrate. There are 3 types of decels. Early decels are at the beginning of a contraction. This type of pattern is almost always head compression. It is a good, healthy and normal response to a baby descending into the pelvic and they are telling us their head is getting squeezed. This communicates to a midwife that a mom may be pushing soon, even if the mom hasn't shown signs yet.



Variable or Random Decels that have no pattern is common when a cord is being squeezed too tightly. A change in mom's position may often remedy this.


Late decels, most commonly, happen when the blood flow between the uterus and the placenta is compromised. It is a reflection of a placental oxygen deficiency. We are looking for a recurrent pattern. Remember, a decel has to last longer than 15 seconds or it is just a variable. If we have established that there are reoccurring late decels, we will recommend a transfer to the hospital for delivery. Oftentimes, they will monitor in the hospital. It doesn't mean an immediate c-section, in most cases. We prefer to have monitoring done in a hospital that is equipped to handle more thorough monitoring and has the ability to act quickly in an emergency with tools that are out of our scope to practice.


There is another pattern, or I should more aptly say "a lack of pattern", that I would like to note. Very rarely, we cannot find a pattern. There may be a lot of variability... in truth, too much variability. The baby's heart rate will be all over the place. We cannot tell where the baseline is because the heartbeat will drop to 110 then jump to the130s, then back and jump to the 150s. There is no 20% frequency anywhere in the monitoring. This heartbeat, if you saw it on a strip, would resemble a pogo stick bouncing. We often don't know the reason for this pattern, but it is another recommended transfer.


When your midwife brings out the doppler to have a quick listen, you will be a little more informed of the conversation the baby is having with her. You can know that even when the heartbeat is a little slower, that she is listening to "when is it slower", "how often is it slower" and "how long is it slower" and "did that baby just kick me" and "oh, I think mom is getting pushy". You will know that your midwife knows that 100 bpm in some labors is a sign to "get ready to catch" and 100 bpm in another labor means "let's transfer". But everytime, we want to walk along side of you and inform you. So always ask questions... because midwives want to hear from you as well.


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