Antenatal women with or without pelvic pain can be characterized by generalized or segmental hypoalgesia in late pregnancy

The aims of the present study were to determine the influence of pregnancy on somatosensory responses in women with or without pelvic/lumbosacral pain. Thirty pregnant women participated and were divided into pain (n = 12) and nonpain (n = 18) groups on the basis of pain complaints and positive pain-provoking tests associated with pelvic or lumbosacral pain during the current pregnancy. In the pain group, 9 reported initial pain in trimester 1, 2 in trimester 2, and 1 in trimester 3. Quantitative sensory testing with pressure pain threshold (PPT), heat pain threshold (HPT), and tactile threshold (TT) was performed once during each of the 3 trimesters at referred pain sites (sacrum, back, and pubis) and no pain control sites (thigh, arm, and sternum). All subjects in the pain group reported back pain, and 91% also had pain at the sacrum and pubis. The pain group exhibited significantly greater pain sensitivity than the nonpain group. The HPT and PPT were higher in trimester 3 as compared to trimesters 1 and 2 (P < .012). The increase in thresholds, or hypoalgesia, was generalized and present at both referred pain and control sites in the pain group, In the nonpain group hypoalgesia was localized to the presumed referred pain sites at the back and sacrum. There were no significant variations in the TT in any trimester. The study demonstrates for the first time that hypoalgesia in late pregnancy is generalized in women with pelvic pain and localized in women without pelvic pain. This suggests that the descending noxious inhibitory system is activated in late pregnancy and is probably more intense and generally activated in women with pelvic pain and only segmentally activated in women without pain. (C) 2002 by the American Pain Society.