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18: Quantitative fetal fibronectin screening at 24 weeks substantially discriminates the risk of recurrent preterm delivery in asymptomatic patients with prior preterm birth

      Objective

      To determine the degree to which a single quantitative vaginal fetal fibronectin (fFN) screen at 24 weeks gestational age (wks GA) discriminates the risk of recurrent preterm delivery (PTD) in an asymptomatic high risk population.

      Study Design

      We performed a secondary analysis of a prospectively collected data set (PREMET study, Shennan et al, BJOG, 2005) in which 900 high risk asymptomatic patients (pts) with singletons underwent vaginal fFN screening at 24 wks. 53 pts randomized to antibiotic intervention were excluded as were pts whose delivery information was incomplete. As > 80% of the remaining pts had a previous PTD, the analysis was focused on this high risk group, and those pts without prior PTD were also excluded. The remaining 572 patients who underwent fFN screening at 24 wks were analyzed, and all outcomes were included. Patients with indicated PTDs were excluded from the spontaneous PTD rate for that GA. All fFN tests were quantified (results not previously reported).

      Results

      The overall spontaneous PTD rate <34 wks was 7.0% (40/571), and the spontaneous PTD rate < 37 wks was 21% (120/571). Rates of PTD at 32-37 wks generated 4 distinct stratified cluster groups (fFN 0, 1-49, 50-199, > 200). As fFN values increased, PTD rates also increased progressively. For example, the rates of PTD < 34 wks in the 4 groups were 5.1%, 15.0%, 22.2%, and 50%, respectively. Compared to the fFN 0 group, the relative risk for PTD < 34 wks was significantly and progressively increased in each group: 2.9 (1.3-6.7, p=.017), 4.3 (1.7-11.1, p=.013), and 9.7 (4.4-21.3, p=.0003). Using delivery probability analysis, similar trends were seen between groups at different GAs between 32-37 wks.

      Conclusion

      In asymptomatic pts with a prior PTD, a single quantitative fFN at 24 wks enables substantial discrimination of recurrent PTD risk which progressively increases for each increase in fFN level. A quantitative fFN provides more precise information regarding the risk of subsequent PTD compared to a standard qualitative fFN test (using a single 50 ng/mL cutoff).