OBJECTIVE: The objective of the study was to investigate temporal changes in interleukin-1 receptor antagonist (IL-1ra) in human cervicovaginal fluid (CVF) in term pregnancy and labor. STUDY DESIGN: CVF was collected weekly from 155 multiparous women from 36 weeks' gestation until labor. High vaginal swabs were collected for microbiology assessment. RESULTS: IL-1ra was decreased in spontaneous term labor, compared with 15-21 and 22-28 days from labor, and was significantly lower at 0-7 days, compared with 15-21 days before labor (P .05, 2-way ANOVA). After subdividing the women, IL-1ra concentrations were 6-fold lower in women who had prelabor rupture of membranes at term than women who had spontaneous labor with intact membranes at 8-14 and 15-21 days before labor (P .05, Student t test). IL-1ra concentrations were not affected by the microbial status of the vagina. CONCLUSIONS: The changes in IL-1ra concentrations observed in the CVF may be linked to the remodeling of fetal membranes leading to rupture.