Preterm delivery: predictive value of cervico-vaginal fetal fibronectin

This study aimed to evaluate the risk of preterm delivery in the asymptomatic obstetric population of L'Aquila by means of fetal fibronectin immunoassay in cervicovaginal secretions.

In this prospective study, 60 asymptomatic pregnant women at low-risk for preterm delivery were followed-up. Fetal fibronectin cervical swabs from the esocervix and posterior vaginal fornix were obtained every second week from 24 to 36 weeks of gestation. Fetal fibronectin concentrations were measured by an enzyme-linked immunosorbent assay with a cutoff level set at 50 ng/ml.

Twelve patients (20%) had at least one positive fetal fibronectin test result. Six women in our study group (10%) were delivered spontaneously < 37 weeks; 4 of these (66%) had at least one positive fetal fibronectin test result (positive predictive value: 33%; sensitivity: 66%) and 3 of these women (75%) had a positive test result between 24 and 26 weeks. The remaining 8 patients with at least one positive fetal fibronectin test were delivered at term or post-term. Forty-eight women always had negative tests and 46 (95.8%) of these were delivered at term (specificity 82%), whereas 2 (4.2%) were delivered prematurely. The negative predictive value of fetal fibronectin as a predictor of term delivery in this low-risk population in 95% with odds ratio = 11.5 (95% confidence interval 1.44 to 110.4), relative risk = 8 (95% confidence interval 1.38 to 59.2) and Fisher Exact Test p < 0.024.

In a population of asymptomatic patients at low risk for prematurity, the occurrence of a positive cervical or vaginal fetal fibronectin test result defines a subgroup at increased risk for preterm delivery, mostly at low gestational age.