A longitudinal study to evaluate pregnancy-induced endogenous analgesia and pain modulation

Background and Objectives: The phenomenon of pregnancyinduced analgesia has been demonstrated in animal models but less consistently in human studies. This study aimed to assess endogenous pain modulation, evaluating inhibitory and excitatory pain pathways, over the course of pregnancy and postpartum. Methods: Healthy pregnant women were approached for participation in this prospective multicenter cohort study. Conditioned pain modulation (CPM), mechanical temporal summation (mTS), and temperature that induced pain 6 out of 10 (pain-6) were assessed toward the end of each trimester of pregnancy (8-12, 18-22, and 36 weeks) and at 6 to 12 weeks postpartum. To assess how pregnancy affects CPM, mTS, and pain-6, a mixed-effects analysis of variance was performed. Results: Thirty-three pregnant women were enrolled. Pregnancy did not significantly impact CPM (F_3,39 = 0.30, P = 0.83, partial η² = 0.02), and therewas no significant difference between CPMscores in the third trimester compared with postpartum. The mTS scores and pain-6 ratings were also not significantly changed by pregnancy (F_3,42 = 1.20, P = 0.32, partial η² = 0.08; and F_3,42 = 1.90, P = 0.14, partial η² = 0.12, respectively). Conclusions: This is the first study to assess CPM and mTS changes in pregnancy and postpartum. Endogenous pain modulation evaluating both inhibitory and excitatory pain pathways did not significantly change during pregnancy or postpartum. Future studies are required to determine themagnitude and clinical significance of pregnancy-induced analgesia.