Understanding TOCO Monitor (Tocodynamometer): How to Monitor and Read Contractions

**Wendy Sutas**, BSN, RN

Electronic fetal monitoring, or cardiotocography, has been used in obstetric medicine for over fifty years. A toco monitor measures contractions, and when combined with a fetal heart monitor, they provide information about fetal well-being. Recently, there has been a professional shift in academic articles to change the term electronic fetal monitoring to cardiotocography, cardio (heart), toco (uterine ), and graphy (recording).⁽¹⁾

Table of Contents

TOCO Number
Fetal Monitor Placement
TOCO Measurement Ranges
Alternative Types of Fetal Monitoring
Caring for Patients with Contraction Pain
Anecdotal Tips
Can a TOCO Number Be Too High?

What is a TOCO (Tocodynamometer) Number?

A toco monitor measures the intensity, frequency, and duration of uterine contractions.⁽²⁾ The nurse places a disk-shaped monitor on the abdomen over the fundus. Tocodynamometers are pressure sensitive and measure the force the contracting uterus exerts on the abdomen. This number appears on the cardiotocograph machine in millimeters of mercury (mmHg).

A toco number is somewhat arbitrary but provides a baseline from which the nurse can see trends in uterine contractions. Toco numbers rise as labor progresses. Contractions becoming more intense causes the number to increase.

The monitor provides a clinical picture of labor over time by producing a strip. The term "strip" refers to the monitor's horizontal graphic display, which historically prints a long "strip" of paper. Contractions appear like hills or waves, identifying the duration in seconds, and the time between contractions is also visible.

The non-invasive nature of a tocodynamometer makes it an easy first choice for monitoring uterine contractions. Nurses use it frequently in the third trimester of pregnancy for the laboring patient, but it also identifies contractions in patients at risk for preterm birth. They apply the toco monitor externally and can remove it intermittently, allowing a laboring woman to walk and have more mobility.

The same qualities that make toco monitors convenient are also a limitation in some scenarios. The patient's position, the belt's tightening, the transducer's age, and obesity can affect the accuracy of the toco number.

Therefore, the toco number provides a framework for understanding uterine contractions. One patient may have a baseline reading of 10 mmHg at rest between contractions, and another may have a baseline of 15 mmHg. Baselines provide a foundation from which to interpret the upcoming data. If the patient begins to feel tightenings or contractions, the toco number should rise from the baseline.

Importantly, toco numbers do not exist in a vacuum. You must consider a toco number and the entire strip within your patient's broader clinical presentation.

Fetal Monitor (Cardiotocograph) Placement

The cardiotocograph simultaneously measures labor contractions and fetal heart rate. This measurement requires the placement of two separate disks on the abdomen, secured with an elastic belt. The pressure sensor captures the contraction data on the monitor display, while a doppler monitor records the fetal heart rate.

The complex relationship between fetal heart rate and uterine contractions reflects fetal well-being during labor. When nurses accurately record these two components, they can identify complications using the various emerging patterns. The strip saves valuable time by presenting emergent and life-threatening conditions. Potential complications include fetal hypoxemia, a lack of oxygen to the fetus in utero, decreased fetal movements associated with stillbirth, abruption, uterine hypertonia, or cord compression. However, the data can also reassure practitioners of fetal well-being and avoid unnecessary interventions, most notably a rush to cesarean section.

Understanding and interpreting this data seems simple, but it requires significant clinical experience, and nurses often need additional training in this modality to develop accurate interpretations.

When positioning a toco monitor, you can palpate the abdomen during a contraction and place it over the tightest point. Using Leopold maneuvers helps you locate the fetus's back, where heart rate conduction is strongest. Nurses reposition these two monitors often when the laboring patient changes positions or the fetus moves in utero.

TOCO Measurement and Ranges

Toco measurements range from 0 mmHg to 100 mmHg. Although the toco number will vary between patients, there are general ranges for different types of uterine activity.⁽³⁾ A normal resting uterus tone is about 10-12 mmHg.

The following table lists types of contractions, defining characteristics, and the normal toco monitor range during different phases of pregnancy and labor.

Latent Phase Contractions	Beginning stage of true labor It may last hours to days before the active phase begins The cervix begins to thin and efface Cervical dilation from 0-6 cm Contractions feel mild to moderate in intensity Contractions last 30-40 seconds and occur every 5-20 minutes TOCO range 25-40 mmHg
Active Phase Contractions	Considered true labor The cervix dilates 6-10 cm as the fetus further descends, preparing for the transition Contractions feel strong and get more intense toward the end of the active phase Contractions last 30-90 seconds and occur every 2-3 minutes TOCO range 50-70 mmHg
Transition Phase Contractions	The cervix fully dilates at 10 cm Contractions remain intense and frequent TOCO range 80-100 mm Hg When actively pushing, the TOCO monitor reads 100 mmHg or higher
Braxton Hicks Contractions	Also known as false labor Irregular frequency It can feel pretty intense Does not produce cervical change May be caused by maternal dehydration; drinking fluids may help TOCO range 5-25 mmHg

Alternative Types of Fetal Monitoring

The accuracy of external tocodynamometers has limitations related to positioning, and therefore, the trace becomes unreliable. The inability to obtain information during labor potentially puts both the mother and fetus in danger. Internal monitoring solves this problem but is not without risk.

Certain high-risk pregnancies and obese patients will require internal fetal monitoring. In obese patients, the external toco monitor cannot reliably pick up contractions through the excessive fatty tissue.

Maintaining continuous internal methods of fetal monitoring outweighs the risk because early identification of abnormal heart rates prevents hypoxic brain injury in the unborn child. Practitioners can then make informed, life-saving decisions when combining both data sets.⁽⁴⁾

Intrauterine Pressure Catheter (IUPC)

An IUPC monitors uterine contraction patterns internally and remains the gold standard for accuracy. The medical provider inserts a small catheter through the cervix into the amniotic space. Membranes must be ruptured or artificially ruptured before insertion. Cervical dilation also needs to be minimal at 1-2 cm. Any internal monitoring increases the risk of infection.

Electrohysterography (EHG)

EHG provides a higher sensitivity than a toco monitor. The practitioner places electrodes on the maternal abdomen to register the electrical activity the contracting uterus produces. It is non-invasive, applied externally, and has a higher sensitivity than a tocodynamometer. It is becoming an option for obese patients and avoids the risks associated with IUPC insertion.

Fetal Scalp Monitoring

Fetal scalp monitoring is another internal device inserted similarly to the IUPC. It is invasive, carries risks, and requires ruptured membranes and a 1-2 cm dilated cervix. However, when fetal well-being is in question, there is no doubt that a scalp electrode provides practitioners with a more precise clinical picture. Healthcare providers attach a small spiral electrode to the skin of the fetal scalp to provide an electrocardiogram (ECG) reflected on the cardiotocograph.

Fetoscope

A fetoscope resembles a regular stethoscope but has an added cone-like attachment. Midwives often use it when assessing fetal heart tones. At about 20 weeks gestation, fetal heart tones are audible by a fetoscope.

Caring for Patients with Contraction Pain

You can consider several interventions⁽⁵⁾ when caring for a patient with contraction pain.

Discuss the birth plan on admission
Provide support and education throughout the birthing process
Allow parents and partners to participate in decision making
The patient may take a warm bath if appropriate
Encourage changing positions and walking when appropriate
Ask your patient to rest between contractions
Perform back massage
Utilize an exercise ball
Guide breathing techniques
Epidural if the patient desires

Anecdotal Tips

When a patient is in active labor, eating and drinking may not be recommended in case of an emergency cesarean section. Many pregnant people welcome ice chips as a simple yet comforting measure.

One of the most important things you can do is take the time to ensure your emergency equipment is working. Test your oxygen, bag, mask, and suction. Check that tubing is functional and attached to the correct wall outlets. Maintain your supplies by having a well-stocked room. Check the radiant warmer and test that it works properly and has a temperature probe. Check all neonatal resuscitation equipment, gather correct size masks, test suction pressure, have intubation equipment available, and stock several size suction catheters and meconium aspirators. Have a delivery table nearby and know which doctor you need to call in an emergency. Locate the crash cart. Support your patient in this monumental event, but always be ready for an emergency. Failed or missing equipment can have dire consequences when time is critical.

Can a TOCO Number Be Too High or Indicate Uterine Rupture?

This question was initially asked in an allnurses forum. The answer is no; the TOCO number alone cannot be too high and indicate uterine rupture.⁽⁶⁾ However, a toco monitor strip can represent signs indicating uterine rupture by displaying overall patterns of uterine contractility. For example, uterine hyperstimulation is five contractions or greater occurring within 10 minutes or a single contraction lasting two or more minutes. Other red flags include decreased contractions or changes to the baseline tone, which must be reported to the OB/GYN immediately.

STAFF NOTE: Original Community Post

This article was created in response to a community post. The comments and responses have been left intact as they may be helpful. Here's the original post:

Quote

I just had a baby (fourth) two months ago, and it was the worst labor ever. The fastest at 4 hours, but yeah, the worst. At the time, my nurse kept shaking her head, telling me that my contractions were off the charts.

That got me wondering, when I got home, what was normal. A few places sited tocodynamometer readings of 120-140 were the average. With the last three kids, I remember the readings got as high as 180/190, and labor was still painfully bearable. But this time, the contractions were measuring 240 PLUS and the nurses were shocked.

So, my question is: Is there ever a reason to worry that the reading is TOO HIGH? I mean, risk of rupture or anything? And what would make them so strong? Any thoughts?

What's truly the normal range?

References

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2. Euliano, T. Y., Nguyen, M. T., Darmanjian, S., McGorray, S. P., Euliano, N., Onkala, A., & Gregg, A. R. (2013). Monitoring uterine activity during labor: a comparison of 3 methods. American journal of obstetrics and gynecology, 208(1), 66.e1–66.e666. https://doi.org/10.1016/j.ajog.2012.10.873

3. Davidson, M. R., London, M. L., & Ladewig, P. W. (2016). Olds' Maternal-newborn Nursing & Women's Health Across the Lifespan (10th ED.). Pearson

4. O'Heney, J., McAllister, S., Maresh, M., & Blott, M. (2022). Fetal monitoring in labour: summary and update of NICE guidance. BMJ (Clinical research ED.), 379, o2854. https://doi.org/10.1136/bmj.o2854

5. Çalik, K. Y., Karabulutlu, Ö., & Yavuz, C. (2018). First do no harm - interventions during labor and maternal satisfaction: a descriptive cross-sectional study. BMC Pregnancy Childbirth, 18(1), 415. https://doi.org/10.1186/s12884-018-2054-0

6. Vlemminx, M. W., de Lau, H., & Oei, S. G. (2017). Tocogram characteristics of uterine rupture: a systematic review. Archives of Gynecology and Obstetrics, 295(1), 17–26. https://doi.org/10.1007/s00404-016-4214-7