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Oral Concurrent Session 8 - Labor & Delivery

Oral Concurrent Sessions

(75) A contemporary assessment of uterine contractility in labor: what is adequate?

Wednesday, February 14, 2024
3:00 PM – 3:15 PM  
Location: Potomac Ballroom C, Ballroom Level
Foundation Awardee
Objective: Labor arrest disorders account for over a third of cesarean deliveries. The diagnosis of arrest requires assessment of contraction adequacy, defined in national guidelines as a minimum of 200 Montevideo units (MVU) in the active phase. This MVU cutoff is derived from a historic cohort of 109 patients in the 1980s. We re-assessed uterine contractility measures in a contemporary cohort of patients with universal intrauterine pressure catheter (IUPC) placement.

Study Design: This was a prospective cohort study of singleton pregnancies ≥37 weeks gestation admitted in spontaneous labor or for induction of labor. All enrolled patients had IUPCs placed at time of amniotomy regardless of preceding labor pattern. For this analysis, we only included patients who had a vaginal delivery. Contraction data were collected by obstetric nurses blinded to outcomes in ten-minute epochs and averaged over 1 hour. MVUs in the 1 hour before 10 centimeters (cm) dilation were assessed to best represent MVU requirements in the active phase of labor.

Results: Of 224 enrolled patients, 190 (84.8%) had a vaginal delivery and IUPC data within 1 hour of 10cm dilation, and were included in this analysis. 170 (89.5%) underwent IOL, 93 (49%) were nulliparas, and 178 (93.7%) received oxytocin. Among those with vaginal deliveries, the median [5th, 95th percentile] MVU was 163 [63, 260]. Using current definitions of adequacy, 7.4% of patients were adequate for all 60 minutes prior to complete dilation and 50% of patients were never adequate in the 60 minutes before 10 cm dilation. Nulliparous patients had a lower median MVU compared to multiparous patients (145.8 [105.8, 188.3] vs 171.7 [128.3, 213.0], P< 0.01).

Conclusion: In this contemporary prospective study with universal IUPC placement not subject to selection bias, there is a wide range of MVUs among patients with successful vaginal deliveries. 50% of patients with vaginal deliveries do not achieve 200 MVUs prior to complete dilation. MVU may be a poor marker of adequacy. If MVUs remain the standard, parity-based stratification of adequacy should be considered.