Association between the serum levels of relaxin and responses to the active straight leg raise test in pregnancy

There is a common belief that the laxity of pelvic joints increases in pregnancy. The hormone relaxin is suggested to be one of the most influential factors implementing this effect. Furthermore, increased laxity is assumed to induce pelvic girdle pain (PGP). The objectives were to examine the serum relaxin levels in pregnancy and to investigate whether relaxin levels relate to symptoms and clinical tests for PGP. Data from questionnaires, clinical tests and blood samples were collected once in pregnancy (gestation week 5–24) from 212 women. Serum from blood samples were analyzed by ELIZA to determine the concentration of relaxin. Self reported symptoms were assessed by Disability Rating Index (DRI) and pain intensity (VAS). Clinical examinations included Active Straight Leg Raise (ASLR) test and pain provocation tests. ANOVA was used to assess the effect of gestation age and multivariable statistics to examine the association between relaxin levels and the symptoms or responses to clinical tests.The serum levels of relaxin varied widely between individuals and were only marginally influenced by the gestation age. There was no association between gestation age and responses to clinical tests or pain intensity, but DRI increased with gestation age. Serum concentration of relaxin showed a significant association to positive score on the ASLR test, but no significant associations to responses to pain provocation tests, pain intensity or DRI.The results indicate that relaxin contributes to laxity of pelvic joints in pregnancy. Yet, no evidence of relaxin having an impact on symptoms or perceived disability was found.