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Your Pregnancy Matters

What fetal heart rate monitoring can – and can’t – tell us

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Dr. Stewart reviewing a patient's fetal heart rate.
Pregnancy is full of tests to monitor how mom and baby are doing: blood and urine tests, genetic screening, ultrasounds, and others depending on your circumstances. Fetal heart rate monitoring also may be performed during your prenatal care, but it certainly will be done during labor and delivery.

Electronic fetal heart rate monitoring keeps track of your baby’s heart rate and helps determine the strength and duration of your contractions. Listening to your baby’s heart rate is one way we can tell how he or she is doing on their way to meet the world.

While fetal heart rate monitoring can alert us to potential problems, it’s also important to remember that a variety of factors, not just heart rate, help us determine how well your baby is doing. Fetal heart rate monitoring is not a crystal ball that predicts your baby’s future health.

I know this from experience. My son’s fetal heart rate looked terrible toward the end of delivery, which led to a few scary moments. However, he perked up shortly after birth and was just fine.

Three ways to monitor fetal heart rate

There are three options to monitor your baby’s heart rate. In the first two types, your baby’s heart rate is continuously recorded, but with the third option, the nurse checks intermittently to see what the heart rate is during labor.

  1. External: This is the most common continuous monitoring we use. Sensors are placed on your belly and held in place with elastic bands. The sensors are connected to a machine that records your baby’s heart rate and uterine contractions. This monitoring works well for most women, but in some cases we just aren’t able to get a good reading with it. This could be because of a woman’s weight, because the baby is small and is hard to keep on the monitor, or because the baby is moving around too much.
  2. Internal: In some high-risk cases, or when we are having problems picking up the baby’s heartbeat with the external monitor, we use an internal monitor. Internal monitoring requires that you are dilated and that the amniotic sac has ruptured. We’ll guide a thin electrode through your vagina and cervix and attach it to your baby’s scalp, then also insert a small tube to monitor the contractions inside your uterus. The electrode and tube are attached to a device that continuously records your baby’s heart rate.
  3. Intermittent auscultation: In a few low-risk situations, we may not need to continuously monitor your baby, and instead use the electronic monitor, a hand-held ultrasound device, or stethoscope against your belly to listen to your baby’s heartbeat at specific intervals. If your physician suspects there is a problem, they may switch to continuous monitoring.
Most women in the U.S. are hooked up to an electronic fetal heart rate monitor – external or internal – continuously throughout labor. Electronic fetal monitoring isn’t painful, but you may find it limits your movements if your hospital doesn’t have the technology to allow you to walk around and still be monitored. At Clements University Hospital, we have the capability to continuously watch your fetus when you are not physically connected to the monitor.

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Fetal heart rate monitor readings

What can fetal heart rate monitoring tell us about your baby?

The main purpose of fetal heart rate monitoring is to alert us if your baby is not getting enough oxygen. We want your baby to come through labor and delivery as smoothly as possible. We don’t want the stress of labor to threaten an infant’s health.

A baby’s heart rate during labor should be between 110 and 160 beats per minute, but it may fluctuate above or below this rate for a variety of reasons. Short bursts of acceleration of the baby’s heart rate are common and indicate that the baby is getting an adequate oxygen supply. Brief decelerations in the baby’s heart rate also can be normal, such as when the baby’s head is compressed while in the birth canal.

If these accelerations or decelerations are not occurring at the stages they should be, or if they are prolonged, it could mean a number of things, such as the umbilical cord is compressed and blood flow to the baby has been slowed. Sometimes a simple intervention such as changing your labor position will improve the situation. If the fetal heart rate results indicate that your baby may be in danger, your physician may recommend an operative vaginal delivery (using forceps or a vacuum device) or a cesarean section.

Limitations of fetal heart rate monitoring

The use of fetal heart rate monitoring has grown dramatically in the past 35 years. In 1980, electronic fetal monitoring was used on 45 percent of pregnant women in labor. By 2002, that number had jumped to 85 percent. Despite the increased use of the technology, we have not seen a reduction in the risk of death and long-term problems from lack of oxygen – such as cerebral palsy. Meanwhile, studies have shown a link between fetal heart rate monitoring and increased interventions – such as C-sections and assisted deliveries using forceps or vacuums – when we are concerned the baby is in danger.

False-positive fetal heart rate monitoring readings – which indicate there is a problem when the baby is actually fine – are common. We classify fetal heart rate readings according to three categories:

  • Category 1: Everything is normal and no action is needed.
  • Category 2: Readings are unclear and require evaluation and surveillance.
  • Category 3: Readings are abnormal and require prompt evaluation and action.
We’re good at identifying when a baby looks normal (category 1). And we’re good at identifying when something is wrong and we need to take immediate action (category 3). In the middle, it gets complicated. Do we act? Do we not act? It’s that big, gray area of category 2 where false-positives often show up.

Because we haven’t been able to demonstrate an improvement in newborn outcomes with conventional electronic fetal monitoring, obstetricians have investigated other possible ways to improve monitoring fetuses during labor. UT Southwestern participated in a study sponsored by the National Institutes of Health that analyzed fetal electrocardiographic information with continuous internal monitoring. Unfortunately, that study did not show improvement in newborn outcomes or a reduction in the number of C-sections performed.

A lot of factors go into assessing a baby’s wellbeing during labor – for example, the mother’s health at the time affects the baby, so we need to take that into account. This is where technology can’t replace a good doctor. If I see a fetal heart rate that doesn’t look great, the first thing I do is examine the patient. You have to put the reading in the context of what’s going on, and a fetal heart rate monitor can’t do that.

Fetal heart rate monitors are useful tools, and babies’ lives have been saved because this technology has alerted us to problems. Still, we need to be aware of their limitations and remember that while a normal reading does not guarantee perfect health later, neither does a concerning reading predict future health problems.

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