Fetal Monitor

Everything You Need to Know About Fetal Monitors

The fetal monitor is a specialized device used by physicians to assess the cardiac function of the baby during labor.

Based on the input of this device, the gynecologist will decide the best approach for delivering the baby, and whether or not any other medical interventions are necessary.

Fetal monitors have revolutionized the fields of obstetrics and gynecology by giving physicians a way to evaluate the health of the baby before and during delivery, which is a crucial step to prevent and reduce fetal mortality.

In this article, we will discuss the beginning of these devices and how we are now using electronic fetal monitoring systems.


Marsac reported the first-ever sign of fetal heart sounds in the 1600s, and then a man named Killian suggested that the health of the fetus could get interpreted by its heart rate. 

This proposition went unnoticed until 1818 when Mayor and Kergaradec proposed the clinical act of auscultating the fetal cardiac activity by placing the ear next to the abdomen of the pregnant female.

In 1833, an English physician named Evory Kennedy published the first guidelines that explain fetal heart rate and the interoperation of the results.

Jumping forward to 1893, where Von Winkel developed criteria to determine fetal distress, using the heart rate, its regularity, passage of feces, and fetal movements.

Since then, numerous modifications were incorporated into the design of the fetal monitor until electronic fetal monitoring appeared in the 1960s. After this event, the electronic fetal monitor became readily available for commercial use, with its first appearance in the United States of America.

How does electronic fetal monitoring work?

Electronic fetal monitoring systems work by detecting the fetus’ heart activity through the womb. The device focuses on the electrical patterns passing through the heart of the fetus to detect any abnormal activity.

Typically, there are two types of fetal monitors that focus on either the continuous evaluation of the baby’s cardiac activity or separated measurements taken before labor.

Regardless of the type of monitoring chosen, both devices work in a similar fashion. Heart activity is detected via an ultrasound probe that is placed on the abdomen of the pregnant woman at the location where the pulse is most ample.

If the physician or nurse opts for the continuous measurement of fetal activity, another probe will be placed with the fetal monitor to record the uterine contractions. This is important since the contracting uterus influences the heart activity of the baby, allowing physicians to interpret both recordings simultaneously.

Indications to use 

Before initiation of labor-stimulating procedures

Making sure that the fetus is in optimal health before conducting any labor-stimulating procedures is essential for the survival of both the pregnant mom and her baby.

For this reason, it is now standard procedure to place a fetal monitor just before labor to assess the viability of the baby.

Before moving the patient

The American Family Physician indicates that moving a hospitalized female patient who is about to give birth requires conducting a recording of the baby’s cardiac activity using a fetal monitor.

Before administration of drugs

Physicians may prescribe several drugs to facilitate the process of labor, including prostaglandin agonists and synthetic oxytocin.

These drugs work by relaxing the cervical canal, which allows the baby to come out more easily. However, the indications to prescribe these drugs vary greatly depending on the state of the baby, hence the need to use electronic fetal monitoring before making this decision.

Before anesthesia

Anesthesia is crucial to perform some surgical procedures, such as C-section. 

However, the anesthetic drug can also alter the respiratory center of the baby, stopping his/her spontaneous breathing mechanism, which will be devastating after birth.

After the admission of the patient

Most hospitals and healthcare facilities utilize a fetal monitor to evaluate the baby’s heart activity at the admission of the patient.

The goal of this step is not therapeutic per se, as it is used to establish a baseline on the condition of the mother and her baby when they were admitted.

If the baby experiences any irregular cardiac function, the physician will compare the two graphs to see the exact changes and hypothesize their origin.

After rupture of the membranes

The rupture of the membrane is the initiation sign of labor. After that, the mother will enter the different phases to deliver the baby.

OB/Gyns use this as an opportunity to assess the baby’s health before coming out to the world.

After a vaginal examination

Despite the importance of the vaginal examination to estimate the duration needed to start labor, it can be traumatic to the baby, primarily if he/she has already descended.

Electronic fetal monitoring will help us be sure that the vaginal examination did not cause any harm to the baby.

When detecting an abnormal uterine activity

Obviously, noticing irregular spasms of the uterus is a sign that requires the use of a fetal monitor.

The reason behind this is that the cardiac activity of the fetus is strongly correlated with the uterine contractions of the mother.

Market-leading brands 

In 2015, the global market for fetal monitors was estimated to be around $2,206 million, which has substantially increased since then.

Experts believe that this market will reach approximately $3,584 million by the year 2022. These numbers reflect the importance of the fetal monitor in ensuring the proper delivery of the baby, as well as protecting him/her from irreversible damage.

Many companies are investing millions of dollars every year to get a bigger share of the market since all economic and medical reports state that the need for electronic fetal monitoring will increase for the foreseeable future.

Here are the major market leaders:

  • Covidien PLC (Ireland)
  • FUJIFILM SonoSite, Inc. (United States)
  • GE Healthcare (United States)
  • Natus (United States)
  • Philips Healthcare (Netherlands)
  • Siemens Healthcare (Germany)
  • Neoventa Medical (Sweden)
  • Spacelabs Healthcare, Inc. (United States)
  • Analogic Corporation (United States)
  • ArjoHuntleigh, Inc. (Sweden)

As you can see, the vast portion of the market is dominated by US companies, which translates to the field, as the need for fetal monitors is the highest in North America.

General specifications

For the general specifications section, we chose GE Healthcare’s Corometrics 170, which delivers accurate recordings of the fetal cardiac activity and takes into consideration the mother’s comfort.

Here are the specifications of the ultrasound device:

  • Technique Pulsed Doppler with autocorrelation processing 
  • Transducer Type 9-crystal 
  • Pulse Repetition 2 kHz (all modes) 
  • Frequency Pulse Duration 92 μs 
  • Transmitter Frequency 1.151 MHz 
  • Spatial-Average Temporal Isata <5 mW/cm2 
  • Average Intensity 
  • Focal 20 dB Beam Area 16.6 cm2, at a range = 7 cm 
  • Peak Instantaneous 1.8 mW/cm2
  • Intensity 
  • Heart Rate Counting Range 50-210 BPM


The fetal monitor is used in non-invasive procedures that accurately detect the electrical activity of the baby’s heart, which is a major factor that determines the prognosis of pregnancy and labor.

These devices keep getting more sophisticated every year, with mostly electronic editions available in the US.

Hopefully, you found this article informative and beneficial.

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