Introduction Elafin, a natural antimicrobial peptide, is an important component of the innate immune system. It is hypothesised that elafin production in cervico-vaginal fluid (CVF) will be altered in women at risk of spontaneous preterm birth (sPTB) associated with inflammation/infection.

Aim To determine the relationship between CVF elafin concentrations and cervical length in women at high risk of sPTB.

Methods Elafin concentrations were measured in 437 CVF samples (taken two-weekly between 14-28 weeks') from 74 pregnant women (asymptomatic, high risk for sPTB).

Controls women who did not develop a short cervix (n=38); cases: women who developed a short cervix <25mm, n=36) and were randomised to either cerclage or vaginal progesterone (400 mg/od). Elafin was measured by ELISA. Logged data were analysed using random-effects interval regression.

Results Concentrations of elafin were higher in the CVF of the short cervix group, regardless of gestation and treatment (ratio 2.71, CI 1.94 to 3.79, p<0.0005). Elafin concentrations predicted cervical shortening from 14 weeks' (n=11, ROC area = 1.00, p=0.0082), and remained high when cervical shortening was first detected (ratio 3.03 CI 1.92-4.81, p<0.0005). Elafin concentrations were unaltered by cerclage or progesterone (ratio 1.28, CI: 0.88-1.87, p=0.196). Raised elafin concentrations <24 weeks' were associated with SPTB <37 weeks (ratio 1.79, CI: 1.05-3.05, p=0.034).

Conclusion These data suggest that CVF elafin concentrations may be useful for the early prediction of sPTB prior to cervical shortening.