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General product and regulatory information only. This page is not medical advice and does not describe how to use a monitor on a patient.
Short answer
A tocodynamometer (toco monitor) is an external uterine contraction monitor: a transducer strapped to the mother’s abdomen that records the duration, frequency and relative pressure of uterine contractions. In US federal regulation it is a Class II device under 21 CFR 884.2720. It tracks contractions only, so it is not a fetal heart rate monitor.
Definition and scope
The US regulation spells the name “tokodynamometer.” 21 CFR 884.2720 defines an external uterine contraction monitor as “a device used to monitor the progress of labor,” and says it “measures the duration, frequency, and relative pressure of uterine contractions with a transducer strapped to the maternal abdomen.” The regulation adds that the device “may include an external pressure transducer, support straps, and other patient and equipment supports.”
That last sentence is the regulatory meaning of the “fetal monitor belt” people search for: the support straps and transducer accessories are named parts of the device description, not a separate product category. (Source: eCFR, 21 CFR 884.2720, checked 2026-10-30.)
How it is used in practice
The regulation’s own description is the sourced summary: the transducer sits against the maternal abdomen, held by straps, and the output is a record of contraction duration, frequency and relative pressure that staff use to follow the progress of labor. Because the wording is “relative pressure,” the regulation does not describe an absolute pressure reading from the external transducer.
Types: external toco, EMG and intrauterine catheter
FDA’s device classification database (openFDA, record updated 2026-10-19, checked 2026-10-31) lists two product codes under 21 CFR 884.2720, both Class 2 in the Obstetrics/Gynecology panel:
| Product code | FDA product name | What the record says |
|---|---|---|
| HFM | Monitor, Uterine Contraction, External (For Use In Clinic) | The classic external contraction monitor, Class 2, not an implant, not life-sustaining. |
| OSP | Uterine Electromyographic Monitor | Intended to pick up uterine EMG signals from surface electrodes on the maternal abdomen; produces a uterine activity tracing and monitors women in labor at term gestation with a singleton pregnancy. |
A third approach, the intrauterine catheter, measures contractions internally and is possible after the membranes rupture. The Cochrane review by Bakker and colleagues notes that inserting an intrauterine catheter carries potential risks for mother and child. It is not an external toco and is not covered by the same product codes above.
Where it matters for clinics and supply decisions
Three sourced points are useful when a supply list or catalogue mentions a toco:
- Regulatory identity. Look for 21 CFR 884.2720, Class II. Perinatal monitoring systems, by contrast, are classified separately under 21 CFR 884.2740 (product code HGM).
- What is included. Per the regulation, the straps and supports are part of the device description. The regulation also names an external pressure transducer as a possible component, so the transducer and straps fall under the same device description.
- External versus internal. The Cochrane review (Bakker JJH et al., 2013, CD006947, PMID 23913521) pooled 3 randomized trials with 1,945 women during induced or augmented labour. It found no differences between internal and external tocodynamometry for maternal or neonatal outcomes; instrumental delivery pooled RR 1.05 (95% CI 0.91 to 1.21). The included trials had mixed risk of bias.
For related equipment, see the guides on the fetal Doppler, the fetoscope and the birthing center supply checklist, and the general explainer what is a medical device.
Common misunderstandings
A toco is not a fetal heart rate monitor
The regulation defines the device by contractions: duration, frequency and relative pressure. Monitoring of the fetal heart is a separate function; the fetal Doppler guide covers one such device.
The reading is relative, not absolute
The regulation says “relative pressure,” so an external toco trace is not described as an absolute pressure measurement.
“Tocodynamometer” and “tokodynamometer” are the same device
Both spellings refer to the external uterine contraction monitor. The CFR uses the “tokodynamometer” spelling.
FAQ
What is a fetal monitor belt?
It is the strap that holds the transducer against the maternal abdomen. 21 CFR 884.2720 lists support straps among the components an external uterine contraction monitor may include.
What does a tocodynamometer measure?
The duration, frequency and relative pressure of uterine contractions, through a transducer strapped to the maternal abdomen (21 CFR 884.2720).
What FDA class is a tocodynamometer?
Class II under 21 CFR 884.2720; openFDA lists product codes HFM and OSP under this regulation.
How do internal and external tocodynamometry compare in the research?
The Cochrane review found no differences between the two types of monitoring for any maternal or neonatal outcome across 3 trials and 1,945 women.
Sources
- eCFR, 21 CFR 884.2720, External uterine contraction monitor and accessories: ecfr.gov, checked 2026-10-30.
- openFDA device classification, regulation number 884.2720: api.fda.gov, record updated 2026-10-19, checked 2026-10-31.
- Bakker JJH et al., Internal versus external tocodynamometry during induced or augmented labour, Cochrane Database Syst Rev 2013;(8):CD006947: PubMed 23913521, checked 2026-10-31.
