DOI: 10.1002/ijgo.71151 ISSN: 0020-7292

Uterine contractile activity thresholds associated with neonatal acidemia at term: A secondary analysis of a randomized controlled trial cohort

Milla Juhantalo, Tuija Hautakangas, Outi Palomäki, Jukka Uotila
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Abstract

Objective

This study identifies clinically relevant thresholds for normal and excessive uterine activity (UA) in relation to umbilical artery (UmA) pH.

Methods

This blinded secondary analysis included 625 term singleton pregnancies from a randomized controlled trial (NCT02941393, ClinicalTrials.gov ) cohort with intrauterine pressure (IUP) monitoring, cephalic presentation, and umbilical cord blood sampling at birth. Measures included IUP expressed as Montevideo units (MVUs), contraction frequency per 10 min, and uterine baseline tone. Associations between UA and UmA pH (≤7.15) or base excess (linear) were assessed using linear and logistic regression and Student's t ‐test.

Results

With an IUP cutoff >250 MVUs, the proportion of neonates with pH ≤7.15 increased from 16.8% to 25.6% (OR 1.68, 95% CI 1.10–2.59; P  = 0.017). Among oxytocin‐stimulated labors ( n  = 579), an IUP cutoff >200 MVUs was associated with an increase in pH ≤7.15 from 14.7% to 21.4% (OR 1.58, 95% CI 1.02–2.44; P  = 0.038). Elevated baseline tone showed a similar association, with the incidence of pH ≤7.15 increasing from 16.6% to 23.6% at a threshold >20 mmHg (OR 1.59, 95% CI 1.06–2.39; P  = 0.025). A significant downward shift in UmA pH distribution was observed at a contraction frequency >5/10 min (7.23 [0.09] vs. 7.22 [0.09]; P  = 0.042), and among oxytocin‐stimulated labors, this shift occurred already at >4/10 min (7.24 [0.08] vs. 7.23 [0.09]; P  = 0.016).

Conclusion

Suggested thresholds associated with neonatal acidemia are IUP ≤250 MVUs, contraction frequency ≤5/10 min, and baseline tone ≤20 mmHg. For oxytocin‐stimulated labors, lower thresholds (IUP ≤200 MVUs and contraction frequency ≤4/10 min) appear safer.

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