taVNS for uterine contraction pain and early recovery after spontaneous vaginal birth: a three-arm randomized controlled trial protocol

Abstract

Uterine contraction pain after spontaneous vaginal birth (SVB) hinders early maternal recovery. Transcutaneous auricular vagus nerve stimulation (taVNS), as a safe, and non-invasive alternative therapy, can alleviate pain and improve sleep and emotion. Although a recent trial has confirmed its benefits after cesarean delivery, direct evidence evaluating the clinical efficacy of taVNS among post-SVB populations remains absent. This is a single-center, prospective, sham-controlled, three-arm parallel-group randomized clinical trial. A total of 144 maternal participants after SVB will be enrolled and randomly assigned in a 1:1:1 ratio to the 1-Hz taVNS group, 20-Hz taVNS group, or the sham taVNS group. All participants will receive routine postpartum care and undergo a 30-minute daily intervention on the left ear for 3 consecutive days, beginning on the day of delivery. The primary outcome is the proportion of participants with a Visual Analog Scale (VAS) pain score ≥ 4 on postpartum day 3. Secondary outcomes include pain intensity and episode characteristics at other time points, rescue analgesia rate, lactation and breastfeeding status, vaginal bleeding, mood, sleep, and adverse events. Electrocardiogram (ECG) data will be monitored before and after each treatment session. This trial will evaluate the efficacy and safety of 1-Hz versus 20-Hz taVNS compared with sham stimulation for moderate-to-severe uterine contraction pain on postpartum day 3 among women after SVB, while assessing its effects on early recovery. Our findings may provide a rationale for scaling up this non-invasive technology in hospital settings, thereby contributing to improved postpartum care outcomes. International Traditional Medical Clinical Trial Registry (ITMCTR), ITMCTR2026001275. Prospectively registered on 7 June 2026.