What is considered an adequate Montevideo Unit (MVU)?

Adequate Montevideo Units (MVU) in Labor Management

An adequate level of uterine activity is generally considered to be at least 200 Montevideo Units (MVU), which should be sustained for a sufficient period before considering cesarean delivery for labor arrest. 1

Definition and Measurement of MVU

• Montevideo Units measure uterine contraction intensity, calculated as the sum of contraction amplitudes (in mmHg above baseline) within a 10-minute window as measured by an intrauterine pressure catheter 2
• MVU quantification provides an objective assessment of uterine activity during labor, especially when oxytocin is being used for induction or augmentation 1

Adequate MVU Thresholds

• 200 MVU is widely considered the minimum threshold for adequate uterine activity during labor augmentation 3, 1
• During oxytocin induction, approximately 91% of women with successful vaginal deliveries achieve at least 200-224 MVU, with 40% reaching at least 300 MVU 1
• For labor augmentation, about 77% of women with successful vaginal deliveries achieve at least 200 MVU 1

Clinical Application of MVU

• Before considering cesarean delivery for cephalopelvic disproportion or failure to progress, uterine activity of at least 200 MVU should be documented 1, 4
• In cases of labor arrest, at least 200 sustained MVU for more than 2 hours is considered insufficient justification for cesarean delivery alone 3
• Studies show that 61% of women experiencing labor arrest for over 2 hours despite at least 200 sustained MVU still achieved vaginal delivery 3

Limitations of MVU Assessment

• MVU measurement is of limited value in determining if a patient is in the active phase of labor, as contractions inconsistently increase in intensity, frequency, and duration throughout the first stage 2
• No abrupt change in contraction characteristics occurs to distinguish when active labor has begun; therefore, cervical dilation pattern remains more reliable for identifying active labor onset 2
• Recent research suggests MVU measurements may have minimal usefulness in nulliparous women with obesity, as MVUs were only minimally responsive to oxytocin dose and were not strongly associated with labor progression or birth route in this population 5

Considerations for Different Patient Populations

• Oxytocin-augmented labor proceeds at substantially slower rates than spontaneous labor, with nulliparas who delivered vaginally dilating at a median rate of 1.4 cm/hour versus 1.8 cm/hour for parous women 3
• In both nulliparous and parous women, the 5th percentile of cervical dilation rate during oxytocin augmentation is 0.5 cm/hour 3
• Women undergoing oxytocin induction typically achieve significantly greater uterine contraction pressures than those receiving oxytocin for augmentation 1

Pitfalls and Caveats

• Relying solely on MVU without considering cervical dilation patterns may lead to premature cesarean delivery decisions 2, 3
• Contractile patterns have been extensively studied but have yielded little to facilitate differentiating normal from abnormal labor 2
• Serial cervical examinations at least every 2 hours are necessary to determine when the rate of dilation increases from the latent phase to the more rapid progression of the active phase 2
• In some populations, particularly nulliparous women with obesity, MVU measurements may not be useful for diagnosing labor arrest 5

When managing labor with oxytocin, achieving adequate uterine activity of at least 200 MVU should be documented before considering cesarean delivery for labor arrest, but this metric should be interpreted alongside cervical dilation patterns for optimal decision-making.