Circulating relaxin and cervical length in midpregnancy are independently associated with spontaneous preterm birth

OBJECTIVE: We sought to examine associations among serum relaxin levels, cervical length, and spontaneous preterm birth (sPTB). STUDY DESIGN: We conducted a case-control study within a cohort of 1080 singleton pregnant women. In all, 38 women (3.5%) delivered spontaneously preterm (< 37 completed weeks of gestation). Relaxin was measured in serum in gestational weeks 12 and 19, cervical length only in week 19. Associations to sPTB were evaluated by logistic regression analysis and receiver operating characteristic curves. RESULTS: Cervical length and relaxin in week 19, but not week 12 were associated to sPTB. There were no correlations between cervical length and relaxin level in week 12 (controls: Spearman rho: -0.07, P = .45; cases: Spearman rho: -0.07, P = .72) or week 19 (controls: Spearman rho: -0.03, P = .77; cases: Spearman rho: 0.04, P = .84). CONCLUSION: There were no correlation between relaxin concentrations and the cervical length, indicating that relaxin is probably not the cause of preterm shortening of the cervix.