Objective: To evaluate clinical risk factors, cervical fetal fibronectin (fFN), cervical length, and mean gray value assessment in predicting of preterm delivery (PTD) in patients with signs and/or symptoms of preterm labor (PTL).
Study design: One hundred and seventeen women with PTL between 24 and 34 weeks of gestation were included. Cervical swabs were tested for fFN using the rapid fFN assay. When 2-dimensional transvaginal ultrasound measurement of cervical length was completed, a region of interest (ROI) of constant size was defined in the midsection of the posterior wall, and the tissue-specific gray scale was determined. The end point were PTDs at <34 and <37 weeks of gestation.
Results: In univariate analysis, the three strongest predictors of spontaneous preterm birth <34 weeks were positive fFN (relative risk [RR] 8.9; 95% confidence interval [CI] 2.6–30.1), cervical length ≤2.5 cm (RR 6.9; 95% CI 1.6–29.7), and a low mean gray value of ≤5.97 (RR 7.9; 95% CI 2.3–27.2). Predictors significantly associated with spontaneous PTD at less than 37 weeks of gestation included previous PTD in multiparas (RR 3.9; 95% CI 1.6–9.5), positive fFN (RR 7.6; 95% CI 3.8–15.3), cervical length ≤2.5 cm (RR 2.6; 95% CI 1.4–5.1) and a low gray scale value of ≤6.54 (RR 4.5; 95% CI 2.3–8.9). In the final regression models used to predict spontaneous PTD <34 weeks and <37 weeks of gestation, both a positive fetal fibronectin (odds ratio [OR] 13.4; 95% CI, 2.5–72.1, P=0.003 vs. OR, 17.3; 95% CI 4.9–61.8, P<0.001) and a low gray scale value (OR 6.3 95% CI 1.3–29.4, P=0.02 vs. OR, 7.1; 95% CI 2–25.2, P=0.003) remained powerful predictors. The RRs of spontaneous PTD <37 weeks has been analyzed by a combination of these significant parameters. Low mean gray value ≤6.54 and negative fFN had a 10.3-fold (95% CI 2–74.5) increased risk of spontaneous preterm birth at <37 weeks. Combination of positive fFN and normal gray level (>6.54), had a higher increase risk of PTD (RR 18.1; 95% CI 4.4–76.7). When both factors were positive, the RR increases to 24.8 (95% CI 6.2–98.7).
Conclusions: Combined use of rapid fFN and cervical gray value analysis improves the diagnostic efficiency and allows identification of women at risk for preterm delivery and in need for further prophylactic/therapeutic intervention.