Uterine activity is quantified by determining the strength and frequency of contractions over a 10-minute period. The strength of each contraction is measured in millimeters of mercury (mmHg) above baseline uterine tone. The Montevideo unit (MVU) is calculated by multiplying the average pressure generated by each contraction (above baseline) by the number of contractions in a 10-minute window. For example, if a patient has contractions averaging 50 mmHg above baseline and experiences four contractions in 10 minutes, the MVU value is 200.
This measurement provides a standardized method for assessing the adequacy of labor and predicting the likelihood of vaginal delivery. Clinicians use MVUs to guide decisions regarding interventions such as augmentation with oxytocin. A sufficient level of uterine activity, typically considered to be between 200 and 250 MVUs, is generally required for effective cervical dilation and fetal descent. The concept was introduced by Roberto Caldeyro-Barcia and Herman Alvarez in Montevideo, Uruguay, hence the name. Their work established a quantitative framework for understanding the physiology of labor and significantly improved the management of labor dystocia.