Methods: Blood samples were collected from 130 gravidas at 22-34 weeks' gestation. The study group consisted of 89 women evaluated for preterm contractions or premature rupture of membranes, and these women were compared with 41 outpatient controls without evidence of labor or infection, chosen by clinicians at the time of routine prenatal visits. Serum interleukin-6 concentrations were measured using a specific enzyme-linked immunosorbent assay kit. Analyses were by the Mann-Whitney U and the Kruskal-Wallis tests.

Results: All 41 control subjects had serum interleukin-6 concentrations less than 8 pg/mL. Sixteen of the 89 study patients had serum interleukin-6 concentrations greater than or equal to 8 pg/mL and 73 had values less than 8 pg/mL. When the serum interleukin-6 concentration was at least 8 pg/mL, the median interval from collection to delivery was significantly shorter than that among study and control subjects with serum interleukin-6 less than 8 pg/mL (5.5 versus 240 and 1801 hours, respectively; P<. 001). The median gestational age at delivery was significantly lower when the serum interleukin-6 concentration was at least 8 pg/mL, compared with study and control subjects with serum interleukin-6 concentrations less than 8 pg/mL (29.6 versus 33.4 and 39.0 weeks, respectively; P<. 001). In patients with preterm contractions, the interval from collection to delivery was significantly shorter when the serum interleukin-6 concentration was at least 8 pg/mL than when it was less than 8 pg/mL (3 versus 600 hours, P<. 001). Similarly, the median gestational age at delivery was significantly lower when serum interleukin-6 was at least 8 pg/mL (29.0 versus 36.1 weeks, P<. 001).

Conclusion: Maternal serum interleukin-6 concentrations appear to be elevated in women destined to deliver prematurely. Measurement of this cytokine may prove useful in treating patients at high risk for preterm delivery.