Diagnosis of intraamniotic inflammation by measuring vaginal interleukin-6 in patients with cervical insufficiency: could amniocentesis be avoided?

BACKGROUND

Cervical insufficiency is a recurrent, passive, and painless dilation of the cervix in the second trimester. The etiology is unclear, but there may be an association with subclinical intraamniotic infection. Interleukin-6 (IL-6) production in the amniotic cavity is induced by bacterial invasion, it is the major proinflammatory cytokine released in response to infection. Although the gold standard method to measure it is through an amniocentesis, the procedure constitutes an invasive technique with several associated risks. The objective of this study is to determine if there is a correlation between intraamniotic and vaginal IL-6 in patients with cervical insufficiency and bulging membranes during the second trimester of pregnancy, in order to avoid an amniocentesis before the rescue cerclage.

METHODS

A cohort study was performed in which all patients with cervical insufficiency and bulging membranes admitted into our tertiary hospital between 2019 and 2020 were included, and a control group of asymptomatic women in the second trimester of gestation where studied at the same time. Patients with bulging membranes underwent an amniocentesis to quantify amniotic IL-6, and a sample of vaginal fluid for vaginal IL-6 determination was obtained from both the study and the control group.

RESULTS

A total of 20 women were included in each group. Median gestational age at diagnosis was 22 weeks in patients with bulging membranes, and 21 weeks in the control group. Vaginal IL-6 in control group (10.875 pg/mL) is much lower than the study group one (1308.77 pg/ml). In patients with bulging membranes, vaginal IL-6 expression was lower in the vagina than in the amniotic cavity [average IL-6 in the amniotic cavity 26890.07 pg/mL, vs 1308.77 pg/mL in the vagina (p < .01)]. Through a Spearman coefficient correlation rank [rho = 0.709 (p < .001)], there is a positive correlation between amniotic and vaginal IL-6 values. The best value of this correlation was calculated with the ROC curve, being the area under the curve 0.929 (CI 95% 0.721-0.995), and the cutoff of point less than 61.4 pg/ml (sensitivity 83.33%; specificity 92.86%). Patients with vaginal IL-6 < 61.4 pg/ml associated a longer latency time between diagnosis and delivery, a higher neonatal weight and a lower perinatal mortality. Rescue cerclage in vaginal IL-6 < 61.4 pg/ml was the best predictor of good pregnancy outcome.

CONCLUSION

There is a correlation between intraamniotic and vaginal IL-6 in patients with cervical insufficiency and bulging membranes during the second trimester of pregnancy. However, further studies are needed in order to considerate the avoidance of an amniocentesis before an emergency cerclage.