Current perception threshold increases during pregnancy but does not change across menstrual cycle.

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It is well known that pregnancy reduces anesthetic requirements in response to various noxious stimuli. However, there have been no detailed reports concerning functional changes in nerve fibers during pregnancy. Using a Neurometer, a recently available commercial quantitative sensory monitor, we measured current perception threshold (CPT) values for three frequencies corresponding to the stimulation of A-beta, A-delta and C fibers on the median nerve in women at several stages: late pregnancy, the follicular phase and the luteal phase. A significant difference in CPT values on A fibers was noted between the gravid and the nongravid women, but, no significant difference in CPT values was noted in any of the nongravid women in the follicular or luteal phases. Our results support the current theory that pregnancy changes nerve fiber conduction, as indicated by an increase in CPT values especially on myelinated fibers, but does not cause changes in CPT values across the menstrual cycle.