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CME Credit Offered
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Recording available 2/16-5/2
Recording available 2/16-5/2
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AIUM Credit
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Abstract Award
Abstract Award
Foundation Awardee
Foundation Awardee

Poster Session 4

Category: Labor

Poster Session 4

(1246) Do first stage uterine contractility measures predict second stage duration?

Thursday, February 12, 2026
3:30 PM - 5:00 PM  
Objective:
National guidelines base first stage arrest on contraction adequacy, defined as ≥200 Montevideo units (MVUs). However, little is known about whether contraction adequacy or other contraction features predict second stage outcomes. We assessed the relationship between first stage uterine contractility measures and second stage duration.

Study Design:
This was a secondary analysis of a prospective cohort of singleton pregnancies at ≥37 weeks’ gestation with intrauterine pressure catheters (IUPC) placed at time of amniotomy. This analysis only included vaginal deliveries. Contraction data, including peak pressure, MVUs, frequency, duration, tachysystole, and resting tone were collected by research nurses in 10-minute epochs for the 1 hour prior to complete dilation. Linear and logistic regression models were used to test the association between these contraction parameters and second stage duration as well as second stage ≥1.5 hours.

Results:
Of 190 patients with IUPC data and vaginal deliveries, 92 (48%) were nulliparous and 31 (16%) had a second stage ≥1.5 hours. After adjusting for parity and infant weight, higher peak pressure and greater MVUs were significantly associated with shorter second stage. Each 1 mmHg increase in peak pressure was associated with a 1.8-minute decrease in second stage (β = –0.03 hr, 95% CI –0.06 to –0.01, p = 0.01), and each 1 MVU increase was associated with a 0.6-minute reduction (β = –0.01 hr, 95% CI –0.01 to –0.001, p = 0.03) (Table). Peak pressure and having at least one 10-minute segment of adequate MVUs were each significantly associated with a lower odds of second stage ≥1.5 hours (Figure). Other contraction features including frequency, duration, resting tone, and tachysystole were not significant.

Conclusion:
Peak contraction pressure and MVUs in the first stage were modestly associated with second stage duration. In contrast, contraction frequency, duration, resting tone, and tachysystole were not. These findings highlight the need to further study measures of contraction strength, rather than frequency, during second stage management.