Changes in birth-related pain perception impact of neurobiological and psycho-social factors.

ABSTRACT

PURPOSE: To analyse post-partum short- and long-term pain sensitivity and the influence of endogenous pain inhibition as well as distinct psycho-social factors on birth-related pain. METHODS: Pain sensitivity was assessed in 91 primiparous women at three times 2-6 weeks before, one to 3 days as well as ten to 14 weeks after childbirth. Application of a pressure algometer in combination with a cold pressor test was utilised for measurement of pain sensitivity and assessment of conditioned pain modulation (CPM). Selected psycho-social factors (anxiety, social support, history of abuse, chronic pain and fear of childbirth) were evaluated with standardised questionnaires and their effect on pain processing then analysed. RESULTS: Pressure pain threshold, cold pain threshold and cold pain tolerance increased significantly directly after birth (all p < 0.001). While cold pain parameters partly recovered on follow-up, pressure pain threshold remained increased above baseline (p < 0.001). These pain-modulating effects were not found for women with history of abuse. While CPM was not affected by birth, its extent correlated significantly (r = 0.367) with the drop in pain sensitivity following birth. Moreover, high trait anxiety predicted an attenuated reduction in pain sensitivity (r = 0.357), while there was no correlation with fear of childbirth, chronic pain and social support. CONCLUSION: Pain sensitivity showed a decrease when comparing post-partum with prepartum values. The extent and direction of CPM appear to be a trait variable that predicted post-partum hypalgesia without being changed itself. Post-partum hypalgesia was reduced in women with a history of abuse and high trait anxiety, which suggests that individual differences in CPM affect childbirth experience.