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Objective: To relate vaginal fetal fibronectin levels in women with symptoms of preterm labor to subsequent spontaneous preterm birth., Methods: Quantitative fetal fibronectin values were calculated from women who participated in two prospective multicenter trials relating fetal fibronectin to subsequent spontaneous preterm birth. The study populations consisted of women who presented with symptoms of preterm labor between 24(0)/(7) and 34(6)/(7) weeks, a singleton pregnancy, intact membranes, no prior tocolysis, and cervical dilation less than 3 cm., Results: The characteristics of the two study populations were similar. In both populations, the rates of delivery within 7, 14, and 21 days after sampling were clustered into three distinct fetal fibronectin groups (less than 40, 40-100, and 100 ng/mL or more). As fetal fibronectin values increased, the risk of subsequent spontaneous preterm birth also increased. Delivery within 7 days of sampling was 0.4%, 3.3%, and 18.2% (trial A) and 1.4%, 8.0%, 30.0% (trial B) as the fetal fibronectin levels increased from less than 40 ng/mL, to 40-100 ng/mL, and to at least 100 ng/mL, respectively., Conclusion: In women with symptoms of preterm labor, an increase in fetal fibronectin from under 40 ng/mL, to 40-100 ng/mL, to at least 100 ng/mL was associated with a progressive increase in the risk of subsequent spontaneous preterm birth. The use of a single fetal fibronectin cutoff of 50 ng/mL for defining a positive test in women with symptoms of preterm labor should be reevaluated.

Objective: To investigate the relationship between fetal fibronectin and bacterial vaginosis, which are associated with an increased risk for preterm delivery., Methods: Researchers for the Pregnancy, Infection and Nutrition Study, a cohort study of pregnant women at three central North Carolina sites, collected genital tract specimens from all enrolled women between 24 and 29 weeks' gestation. Among women with last menstrual periods between March 10, 1995, and August 15, 1996, 868 pregnancies were eligible for this analysis. Fetal fibronectin was assessed by a dipstick immunoassay kit. Bacterial vaginosis was evaluated by Nugent-scored, Gram-stained vaginal smears (scores of 7-10 considered positive)., Results: Overall, 6.3% of women had positive fetal fibronectin test results, and 18.8% had bacterial vaginosis. The unadjusted relative risk (RR) of fetal fibronectin-positivity comparing women with bacterial vaginosis to those without bacterial vaginosis was 1.6 (95% confidence interval [CI] 1.1, 2.5). Using multiple logistic regression to adjust for race, maternal age, parity, and location of care, women who had bacterial vaginosis and smoked at the time of recruitment were at substantially increased risk of fetal fibronectin-positivity (RR 7.8, 95% CI 2.2, 27.8) compared with smokers without bacterial vaginosis. Among nonsmokers, bacterial vaginosis was not associated with fetal fibronectin-positivity (RR 1.0, 95% CI 0.4, 2.4). These results were essentially unchanged after adding the requirement of vaginal pH exceeding 4.5 to the bacterial vaginosis definition., Conclusion: Fetal fibronectin was associated positively with bacterial vaginosis, but only among women who smoked. These results might provide clues as to the biologic relationship between smoking, infection, and preterm delivery.