Research Implications and recommendations
Our data are among the first to suggest a link between intrauterine resting tone during labor and neonatal outcomes. We hypothesize that this is a result of persistent utero-placental hypoperfusion during labor due to limited recovery of uterine and spiral artery blood flow between contractions. However, this hypothesis will need to be tested with future clinical and mechanistic studies. The most relevant and urgent research directions to consider are whether duration of elevated intrauterine resting tone affects neonatal outcomes and to determine a more precise definition of “elevated” resting tone, rather than our empiric cutoff of >75th percentile. Additionally, studies examining whether any interventions, such as positional changes or intermittent pushing during second stage of labor, can decrease intrauterine resting tone and subsequently fetal morbidity, are needed.
We found that induction of labor, which applied to 58% of patients in the cohort, was less common among women with elevated resting tone. Similarly, women with elevated resting tone were less likely to receive oxytocin and had lower maximum doses of oxytocin during their labor. Despite fewer interventions, women with elevated resting tone were more likely to have a vaginal delivery. These findings suggest that higher resting tone may be a surrogate for more efficient uterine contractility and labor. However, since women in this cohort had an indication for IUPC placement, most likely due to dysfunctional labor, these findings need further assessment in a non-biased cohort. Further research is needed to determine the association between elevated resting tone, uterine contractility and labor progress.