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The interleukin-6 -174 single nucleotide polymorphism: Cervical protein production and preterm delivery

      Objective

      To determine the associations between preterm delivery (PTD), cervical fluid interleukin-6 (IL-6) concentration, and the single nucleotide polymorphism at position -174 in the IL-6 gene (allele 1 “G”; allele 2 “C”). Allele 2 is associated with decreased secretion of IL-6 in vitro.

      Study design

      Cervical fluid samples were obtained with pre-weighed cellulose wicks from women 23-32 weeks gestation with symptoms of preterm labor and intact membranes. Concentrations of IL-6 were determined with a commercial ELISA. IL-6 genotyping was performed on DNA obtained from peripheral or cord blood using a PCR-RFLP technique.

      Results

      137 women were enrolled, and complete information was available for 126. For women without, heterozygous for, and homozygous for allele 2, PTD rates were 17/67 (25%), 14/49 (29%), and 4/10 (40%) (P = .62). For the IL-6 concentrations, 30 subjects were excluded because of staining of the cervical wick with blood. For women delivering preterm (n = 23) and at term (n = 73), respectively, mean ± SD concentrations of IL-6 were 12.04 ± 38.06 and 3.97 ± 4.05 ng/mL (P = .07). For women with spontaneous PTD (n = 19) and all others (n = 77), respectively, IL-6 levels were 13.98 ± 41.79 and 3.91 ± 3.98 ng/mL (P = .04). For women without (n = 48), heterozygous for (n = 39), and homozygous for (n = 9) allele 2, IL-6 concentrations were 4.37 ± 5.77, 8.59 ± 29.06, and 2.40 ± 2.15 ng/mL (P = .50). Neonatal IL-6 genotype was not associated with PTD or cervical IL-6 levels (data not shown).

      Conclusion

      Cervical fluid concentrations of IL-6 were elevated in symptomatic women destined to have a spontaneous PTD. The gene dosage of maternal IL-6 -174 allele 2 was not associated either with increased cervical fluid concentration of IL-6 or with risk of PTD.