Clinical Implications and practical recommendations
Elevated baseline intrauterine tone noted during labor prompts questions regarding subsequent labor management. Our data show that elevated intrauterine resting tone is associated with neonatal compromise. We propose that this be considered during management of labor close to delivery. While the impact of this finding is not robust enough for us to suggest immediate or emergent delivery due to fetal concerns, the study should be used to interpret IUPC data in the context of labor progress, duration, and fetal tolerance.
Elevated intrauterine tone among patients in the second stage provides a context for potential intervention. Oxytocin augmentation is commonly continued from the first stage of labor into the second stage, however, it remains unclear if additional increased expulsion “power” is necessary to effect vaginal delivery following complete dilation. Oxytocin has known risks including fetal acidemia especially when used during the second stage [24]. Vlachos et al investigated the impact of stopping oxytocin infusions once active labor has been achieved and found that less cases of non-reassuring fetal heart rates were observed [25]. However, literature specifically evaluating need for oxytocin during the second stage is needed to determine the potential safety of continuing a common obstetrical practice. Similarly, we were unable to assess effects of elevated resting tone specifically during the first stage and cannot make conclusions regarding effects on neonatal morbidity outside the context of second stage of labor.
Incidence of lower umbilical cord pH has been associated with longer second stage. A meta-analysis from 2020 found a RR 2.00 (95% CI 1.30-3.07) [26]. Our data suggest that longer exposure to elevated resting tone is also associated with fetal acidemia and may compound the effects of prolonged second stage. Therefore, practice patterns to shorten the second stage of labor such as immediate pushing, manual rotation of occiput posterior position, and traditional coached pushing may also be employed to reduce time the fetus spends exposed to elevated pressure [27-30].