Reasons Doctors Use Fetal Heart Monitors

Fetal heart monitor strapped to woman's abdomen

A fetal heart monitor can detect your baby's heartbeat beginning as early as the 9th or 10th week of pregnancy. A normal heartbeat isn't a guarantee that the baby will be healthy, but it is a reassuring sign.

How a Fetal Heart Monitor Works

Fetal heart monitors first came into use in the 1950s. Since then, it has become common to check the fetal heart rate as part of routine prenatal visits. The heart rate is also monitored during labor.

A fetal heart monitor uses a technology called doppler ultrasound to use sound waves to detect blood flow. As the unborn baby's heart beats, blood is pushed out in pulses. Doppler monitors can project the baby's heartbeat as an audio signal or graph. A similar technology is used to create ultrasound pictures of an unborn baby.

At Your Prenatal Visits

Hearing the baby's heartbeat for the first time is one of the most exciting moments in a pregnancy! And, it can be done with a very simple device. An office model of a fetal heart monitor usually looks like a little metal box, with a short cord leading to a monitoring wand about the size of a ball point pen. The doctor or midwife will place some gel on your belly to help transmit the sound and then press the wand against your skin. He/she may need to move the wand around a bit to find the heartbeat. You'll know when you hear it: a pulsing, rushing sound that is fast and steady. The fetal heart rate is significantly faster than your own.

Checking the fetal heart rate at a prenatal visit has two primary purposes:

  • It confirms that your unborn baby is still alive and developing.
  • It helps make sure that the heart rate is normal. (Very fast or very slow fetal heart rates signal that something may be wrong with the fetus.)

During Labor

If you give birth in a hospital, monitoring the fetal heart rate will probably be part of your care during labor. A monitor, encased in a plastic disk a few inches in diameter, will be placed over your belly and held with an elastic strap. A second monitor will measure the timing and strength of your contractions. Wires from the monitors will go to a machine which shows the heartbeats and contractions on a screen. You can expect your nurse to print out the readings periodically. He/she will place them in your chart so that your doctor will see them. If there is any cause for concern, the nurse should contact the doctor right away.

Occasionally, your doctor or midwife will choose to use an internal monitor. This involves inserting a monitoring wire through your vagina and into your uterus, where it is attached to the baby's scalp. A second device measures your contractions from inside the uterus. Internal monitors are usually used when there is concern about the baby's well-being and an external monitor cannot give precise enough information.

Interpreting the Readouts

Interpreting the monitor's readouts is a special skill that requires both study and experience. During labor, the unborn baby's heart rate can be quite changeable even when everything is normal. The beats, which appear as peaks and valleys on a graph, will vary in shape. Some of the changes are worrisome; some are not. It's easy to imagine something's wrong when it isn't.

For some women, it's best not to watch the monitor at all! It can add to your stress level, and it can be frustrating not to know what is normal. If you do want to watch the monitor, here are some very basic things to look for:

  • A heartbeat that is very fast. This is called tachycardia, and it can signal fetal distress. Remember, though, your baby's heartbeat is normally going to be much faster than your own.
  • A heartbeat that is very slow. This is called bradycardia.
  • Lack of variation from beat to beat. The beats should not all look exactly alike; it's concerning if they do. However, lack of variability can be normal under some circumstances.

Home Monitors

Do you want to be able to hear your baby's heartbeat at home? Would you like to share the experience with your parents, friends, or others who can't come to your prenatal visits? It's possible to rent or buy your own fetal heart monitor. You can find ones that count the heart rate and even record the heartbeat for playback later. A web search for "fetal heart monitor" will bring up a number of companies that sell or rent monitors.

Fetal heart monitors are prescription devices, so you'll need approval from your care provider. Doppler ultrasound is considered safe, but doctors have not studied frequent home use.

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Reasons Doctors Use Fetal Heart Monitors