Impact of oxytocin discontinuation on fetal heart rate and uterine contractility: A pre-specified ancillary analysis embedded within a randomized trial.
INTRODUCTION: Oxytocin is widely used to augment uterine contractions during labor. However, its use has been associated with fetal heart rate (FHR) abnormalities and neonatal morbidity, which may be reduced by discontinuing oxytocin during labor. We aimed to assess the impact of oxytocin discontinuation at the onset of the active phase of labor on FHR patterns and uterine contractility. MATERIAL AND METHODS: This study is a pre-specified ancillary analysis of the STOPOXY trial, a multicenter, randomized, open-label, controlled superiority trial conducted in 21 French maternity units between January 2020 and January 2022, which aimed to assess the impact of oxytocin discontinuation during active labor on neonatal morbidity. Participants who received oxytocin before 4 cm dilation were randomly assigned (1:1) to either oxytocin discontinuation or oxytocin continuation. For the present analysis, we included women from the per-protocol discontinuation group of the parent trial. Inclusion was restricted to the six centers with electronic cardiotocography storage where valid cardiotocography recordings were available for at least 1 h before and 1 h after oxytocin discontinuation. Using a paired before-and-after design, FHR parameters (classified according to FIGO criteria) and uterine activity were compared during the 60 min preceding versus the 60 min following oxytocin discontinuation by independent obstetricians blinded to neonatal outcomes. Changes in FHR pattern were categorized as no change, improvement, or deterioration. RESULTS: 284 women fulfilled the eligibility criteria. Following oxytocin discontinuation, mean FHR increased (135 vs. 137.5 bpm; p < 0.002) and FHR variability significantly changed (p = 0.010), with a lower rate of reduced variability (3.9% vs. 2.5%) and a higher rate of normal variability (48.2% vs. 53.3%). The proportion of tracings with decelerations significantly decreased (64.1% vs. 48.6%; p < 0.001). Uterine activity decreased, with fewer uterine contractions (4.0 vs. 3.5 contractions per 10 min; p < 0.001). CONCLUSIONS: Among women receiving oxytocin during early labor, discontinuation at the onset of the active phase was associated with improved FHR patterns and reduced uterine activity, suggesting a lower fetal stress and tachysystole. Further studies are needed to assess whether these changes affect labor management or maternal experience.