In a term pregnant woman in active labor, what tocodynamometer (TOCO) values—contraction frequency, duration, amplitude, and Montevideo units—are considered normal, and what thresholds indicate insufficient or excessive uterine activity?

TOCO Monitor Values During Labor

Normal uterine contractions during active labor are defined as ≤5 contractions per 10 minutes (averaged over 30 minutes), with tachysystole diagnosed when >5 contractions occur in a 10-minute period. 1

Understanding TOCO Limitations

External tocodynamometry has significant constraints that clinicians must recognize:

• TOCO cannot accurately measure contraction strength or amplitude—only frequency and approximate duration can be reliably assessed. 2
• The external transducer provides limited information for determining labor phase or adequacy of uterine activity, as contraction patterns rise inconsistently without abrupt changes at phase transitions. 3
• An intrauterine pressure catheter (IUPC) must be used if accurate assessment of contraction strength is clinically necessary, as external transducers have fundamental limitations in measuring amplitude. 1
• Research confirms that TOCO has only 54% sensitivity for identifying individual contractions compared to IUPC, with high timing variability (±10 seconds). 4

Normal TOCO Parameters

Contraction Frequency

• Normal: ≤5 contractions per 10 minutes (averaged over 30 minutes). 2, 1
• Tachysystole: >5 contractions per 10 minutes (averaged over 30 minutes), which must be qualified by presence or absence of fetal heart rate decelerations. 2, 1
• The outdated term "hyperstimulation" should be abandoned. 2

Assessment Beyond Frequency

When evaluating TOCO tracings, clinicians should assess multiple characteristics:

• Rate and rhythm of contractions. 2
• Duration of each contraction (TOCO can measure this). 2
• Resting tone between contractions. 2
• Intensity cannot be reliably measured by external TOCO—palpation or IUPC is required. 2

Critical Clinical Pitfalls

What TOCO Cannot Tell You

• Contraction patterns do not reliably distinguish latent from active labor or differentiate true from false labor. 1
• Montevideo Units and manual palpation provide limited diagnostic value for distinguishing labor phases. 3
• Contraction intensity, frequency, and duration cannot reliably identify the onset of active labor—diagnosis must be based on accelerating cervical dilation rate through serial examinations. 3

What Actually Matters for Labor Assessment

• Serial cervical examinations remain the gold standard for assessing labor progress, not contraction quantification alone. 1
• Active labor is identified solely by an accelerating cervical dilation rate detected through serial vaginal examinations performed at least every 2 hours. 3
• Normal active-phase dilation rates are ≥1.2 cm/hour for nulliparous and ≥1.5 cm/hour for multiparous patients. 3

When to Use IUPC

An intrauterine pressure catheter should be considered when:

• Accurate contraction strength assessment is clinically necessary (e.g., evaluating adequacy of oxytocin augmentation). 2, 1
• Obesity prevents successful palpation of contractions. 2
• Decision-making about oxytocin dosage requires objective data, though quantitation of uterine activity has uncertain value for this purpose. 2

Montevideo Units: Limited Clinical Utility

• Studies have failed to prove the value of Montevideo Units for diagnosis and treatment decisions. 2
• Quantitation of uterine activity is not considered useful in aiding decision-making about oxytocin administration or dosage. 2
• The broad spectrum of contractility patterns associated with both normal and dysfunctional labor makes selecting cases that would benefit from ecbolic drugs often impossible. 2

Practical Management Algorithm

1. Monitor contraction frequency via TOCO to ensure ≤5 per 10 minutes. 1
2. Assess for tachysystole and qualify by presence/absence of fetal heart rate decelerations. 2, 1
3. Do not rely on TOCO alone to determine labor phase or adequacy of contractions. 3, 1
4. Perform serial cervical examinations every 2 hours once active labor suspected to track dilation rate. 3
5. Use palpation or IUPC if contraction strength assessment is needed. 2
6. Plot cervical dilation on a partogram to visualize progress and detect deviations from normal rates. 3