Objective: We investigated the potential roles of relaxin and subclinical intra-amniotic inflammation by quantitating amniotic fluid relaxin and interleukin-6 concentrations for the prediction of outcome of rescue cerclage in women with cervical incompetence.
Study design: Cervical incompetence was diagnosed when cervical dilatation exceeded 2 cm with intact but bulging membranes and no detectable uterine activity. Each woman underwent amniocentesis to facilitate the performance of a rescue cerclage between 15 and 27 weeks of gestation (n=40 women). Forty-five additional women who underwent amniocentesis for chromosomal testing between 16 and 27 weeks of gestation served as a control group. All control patients were delivered of chromosomally normal infants at>37 weeks of gestation. All cases and control patients were singleton gestations. Interleukin-6 and relaxin were determined in all amniotic fluid samples by enzyme-linked immunosorbent assay.
Results: Amniotic fluid interleukin-6 levels were significantly higher in women with cervical incompetence than in control patients (control patients, 50.4 pg/mL [range, 19.4-97.4 pg/mL] vs cervical incompetence patients, 5459.1 pg/mL [range, 1131.4-14425.7 pg/mL] ; P < .001). In contrast to interleukin-6, relaxin levels did not differ between the 2 groups (control patients, 67.5 pg/mL [range, 35.1-153.5 pg/mL] vs cervical incompetence patients, 45.6 pg/mL [range, 30.1-75.5 pg/mL]; P=.061). There was a significant difference in interleukin-6 levels in women with shorter latencies (P < .01 for all latency intervals that were examined: delivery within 24 hours, 3 days, 7 days, before 33 and 37 completed weeks of gestation). Linear regression analysis with the use of the latency interval from cerclage to delivery as the dependent and with interleukin-6 as the independent variable revealed a significant inverse relationship (r=-0.62; P < .001 after log transformation of interleukin-6). There was no relationship on regression analysis between relaxin and the latency interval.
Conclusion: Amniotic fluid interleukin-6 is increased in patients with cervical incompetence, which suggests that subclinical inflammation may contribute to cervical incompetence. Further, an elevated interleukin-6 level predicts a cerclage short-latency interval between cerclage and delivery. In contrast with interleukin-6, amniotic fluid relaxin does not appear to contribute to cervical incompetence-induced cervical dilation.