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      I thank Dr van Baaren and colleagues for their letter concerning the meta-analysis and editorial of fetal fibronectin testing in women with symptoms of preterm labor.
      • Berghella V.
      • Saccone G.
      Fetal fibronectin testing for prevention of preterm birth in singleton pregnancies with threatened preterm labor: a systematic review and metaanalysis of randomized controlled trials.
      • Macones G.A.
      Fetal fibronectin testing in threatened preterm labor: time to stop.
      I believe the purpose of their letter is to point out that observational studies can also be used to assess the performance of diagnostic tests. To support this argument, the authors cite their own work, which was an observational study of how fetal fibronectin and cervical length could be used to risk-stratify women with symptoms of preterm labor.
      • van Baaren G.J.
      • Vis J.Y.
      • Wilms F.F.
      • et al.
      Predictive value of cervical length measurement and fibronectin testing in threatened preterm labor.
      They suggest, based on careful analyses of their own data, that the combination of cervical length and fibronectin results could reduce the number of referrals and admissions to perinatal centers in 10% of all women…. Such a reduction would also result in fewer medications side effects, less maternal stress, and lower health care costs.
      All of this of course sounds terrific, but I would point out the words “could” and “would” in the above sentence. Yes, this algorithm could, in theory, result in many things. What we need to know is not what could happen, but rather what actually does happen. How do physicians actually use these tests in real life? What do they do with the results? How does the test influence use of medications and admission? This is where the clinical trial data become important, and the results of the meta-analysis by Berghella and Saccone
      • Berghella V.
      • Saccone G.
      Fetal fibronectin testing for prevention of preterm birth in singleton pregnancies with threatened preterm labor: a systematic review and metaanalysis of randomized controlled trials.
      are clear and unambiguous.
      I do agree with the authors that observational studies are very useful for determining the potential utility of a diagnostic test. But in the case of fetal fibronectin, we have to move away from theoretical musings of what may happen, and focus on what does happen.

      References

        • Berghella V.
        • Saccone G.
        Fetal fibronectin testing for prevention of preterm birth in singleton pregnancies with threatened preterm labor: a systematic review and metaanalysis of randomized controlled trials.
        Am J Obstet Gynecol. 2016; 215: 431-438
        • Macones G.A.
        Fetal fibronectin testing in threatened preterm labor: time to stop.
        Am J Obstet Gynecol. 2016; 215: 405
        • van Baaren G.J.
        • Vis J.Y.
        • Wilms F.F.
        • et al.
        Predictive value of cervical length measurement and fibronectin testing in threatened preterm labor.
        Obstet Gynecol. 2014; 123: 1185-1192

      Linked Article

      • Randomized clinical trials are not always the best way to assess diagnostic tests: the case of fetal fibronectin testing
        American Journal of Obstetrics & GynecologyVol. 218Issue 1
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          Recently, Berghella and Saccone1 published in this journal a meta-analysis on fetal fibronectin as predictor of preterm birth. In this meta-analysis, the authors concluded that women assigned randomly to the knowledge of fibronectin results did not have reduced preterm birth rates compared to a control group. In addition, both groups had similar rates of hospitalization, and use of tocolytics and steroids. Mean hospital costs were even slightly higher in the fetal fibronectin group. This conclusion was based on 6 randomized clinical trials (RCTs) reporting on 546 women with threatened preterm labor; 13% of the included delivered within 1 week after presentation.
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