Serum relaxin, symphyseal pain, and back pain during pregnancy

OBJECTIVE: Our purpose was to study the relationship between serum relaxin levels and back pain during pregnancy. STUDY DESIGN: A prospective clinical cohort study with repeated examinations was performed. RESULTS: There was an initial increase of relaxin levels until a peak value at the twelfth week followed by a decline until the seventeenth week. Thereafter stable serum levels around 50% of the peak value were recorded. Three months after delivery serum relaxin was not detectable. There was a significant correlation between mean serum relaxin levels during the pregnancy and symphyseal pain or low back pain occurring during late pregnancy as measured by medical history or pain-provoking test. CONCLUSION: Relaxin is known to remodel pelvic connective tissue in several mammalian species during pregnancy. The current data suggest that relaxin might be involved in the development of pelvic pain in pregnant women.