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Maternal Heart Rate Mistaken for Fetal Heart Rate

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Nurses insisted she push in semi-sit position. HR dropped below 100 (80ish). 15 min. into 2nd stage, doc is talking possibility of C. I suggest squatting. In this position, HR stays above 100, ranging from 120 to 160 - great variability, but she can't stay like this forever. Everytime she pushes in a sitting position, HR drops. After a total of about 40 minutes, doc explains that only the caput is coming through and molding. That in conjunction with low HR and late decels puts her back on the operating table under general.

My first thought when I read this was that the monitors were picking up the mom's heart rate, instead of the baby's. (This could only be happening if they were using an external monitor rather than an internal monitor. This is one reason why the midwife who trained me as a labor coach suggested *always* going with an internal monitor before a cesarean for "fetal distress".)

There is a very large artery running across the lower abdomen. I believe it's the external iliac artery. It happens that as the baby starts to descend and rotate into position for birth, typically either in late first stage or early second stage, the place where the baby's heart rate is heard best will cross the mom's external iliac artery, thus starting to pick up her heart rate. The sudden drop in heart rate is often associated with a contraction because during the contraction, the baby descends out of the picture, and the monitor picks up *only* the mom's heart beat.

Ways to tell if this might be happening:

The "drop" in the baby's heart rate is very sudden, rather than a gradual path that you can follow on the monitor.

The alleged baby's heart rate is beating exactly the same as the mom's. Feel her pulse to see. Anytime the numbers you're getting are in the 80's or 90's, consider the possibility that this is really the mom's pulse.

Fiddle with the sensor pad. Move it an inch one way or the other and see if you pick up a different heart beat. I know this is probably impractical during a contraction, so ask if it's OK to adjust it just before you expect the next contraction, move it a little further down and towards the center, the path the baby's heart should be taking, and see if you pick it up normally during the next contraction.

Fetal heart rate variabilities are complex, but it's worthwhile learning them. In particular, it is *essential* to be able to recognize a normal "early decel" pattern. Typically, the heart rate decelerates as an exact mirror image of the contraction on the monitor strips. What is happening is that the pressure on the baby's head is causing a neurological response that is *completely* normal. It might even be considered a *good sign* that there are effective contractions molding the baby's head. In this particular case, it might be that there was adequate pressure on the baby's head *only* when the woman was squatting, and that there was less pressure in the semi-sitting position; it might really have been the baby's heart rate they were picking up, although a sudden drop to the 80's is definitely unusual.

There's so much information that is being left out of this picture. Was the baby recovering quickly from the contractions? Did the heart rate shoot right back up to "normal" after the contraction? In particular, you're looking for sudden discontinuities. It's very unusual for a heart rate to jump 30 points or more in less than 5 seconds.

The only ominous type of deceleration is what's called a "late decel", where the heart rate doesn't start dropping until some time after the contraction begins, and the heart rate doesn't climb back up to pre-contraction levels until some seconds (more than 5, often up to 20 or 30) after the end of the contraction. This means that it is taking the baby a while to recover from the stress of the contraction and that there may be some real problems.

And, of course, it's important to remember that the "stress" of the contraction is the decreased oxygen input. Anything that increases this stress, such as Olympic-style pushing, pitocin, increased anxiety, will contribute to the problem. Help the mom to follow the contraction with a *big* cleansing breath and then to breathe slowly and deeply as much as possible.

This Web page is referenced from another page containing related information about Monitoring Fetal Heart Rate/Decels


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