Aims: Both acute placental inflammation and positive mid-gestational cervico-vaginal fetal fibronectin assays have been independently correlated with preterm delivery. We conducted this study to examine the relationship between positive mid-gestational fetal fibronectin (fFN) assays and histological evidence of acute placental inflammation at delivery among women presenting with symptomatic preterm labor. Methods: This retrospective chart review included women who underwent cervico-vaginal fFN testing for preterm contractions between 24-34 weeks gestation and also had placental histological analysis after delivery. Women with a multiple gestation, cerclage, preterm premature rupture of membranes, intercourse or vaginal bleeding within 24 h before the assay were excluded. The primary outcome was histological evidence of acute placental inflammation defined as acute chorioamnionitis, acute deciduitis, funisitis, or microabscess formation. Results: Of 82 women who met all study inclusion criteria, 45% were fFN positive. Women with positive assays were no more likely to have histological evidence of acute inflammation noted at birth than women with negative assays (45% vs. 26%, P=0.07). The assay had a sensitivity of 58.6%, specificity of 62.3%, positive predictive value of 46.0%, and negative predictive value of 73.3% for predicting acute inflammation at delivery. Conclusions: No association exists between positive fetal fibronectin assays and acute histologic placental inflammation at birth. [ABSTRACT FROM AUTHOR]