Sterile water injections for managing abdominal labour contraction pain: A randomised double blind placebo-controlled trial

BACKGROUND: Sterile water injections have been demonstrated to effectively manage back pain experienced during labour with no side effects other than the administration pain. Abdominal labour pain differs to back pain in location and likely physiological derivation. It is not known if sterile water injections would be efficacious in the relief of abdominal labour contraction pain. OBJECTIVE: To assess the efficacy of sterile water injections to reduce abdominal labour contraction pain. DESIGN: A two-arm superiority randomised placebo-controlled trial. SETTING: A referral maternity hospital in Brisbane, Australia. PARTICIPANTS: Women in spontaneous or induced labour at term requesting analgesia. METHODS: Between April 2022 and November 2023 consenting participants were assigned (1:1) by an independently generated randomisation schedule to injections of either sterile water or saline placebo. The primary outcome was the difference between groups in self-reported visual analogue pain score at 30 min following allocated treatment. Secondary outcomes included use of pharmacologic analgesia following allocation. Analysis was by intention to treat. RESULTS: 160 women were randomised to sterile water injections (n = 81) or injections of saline placebo (n = 79). Seven participants withdrew prior to treatment. Primary outcome data was provided by 68 women (intervention) and 64 (placebo). The mean visual analogue scores at 30 min were: intervention: 52.13 mm (with 100 mm indicating worst conceivable pain) and placebo: 71.14 mm; mean difference: -19.00 mm (95 % Confidence interval (CI) -26.10 to -11.91). Pain scores in the secondary repeated measures model at 60 min post treatment were (61.28 mm vs.76.15 mm) -14.84 (95 % CI -22.23 to -7.46). There was no difference in pain scores at 90 min, use of other pharmacological analgesia, or maternal or neonatal outcomes. CONCLUSION: Sterile water injections provided a statistically significant reduction in pain when compared to a placebo for up to 60 min following treatment. However, the use of other pharmacological analgesia such as epidural did not differ between groups. TRIAL REGISTRATION: The trial is registered at the Australian and New Zealand Clinical Trials Registry (Trial ID: ACTRN12621001036808). Registration date 5/08/2021. First recruitment 29th April 2022.