In this edition of the American Journal of Obstetrics & Gynecology , Berghella and Saccone report the results of a systematic review and meta-analysis of the randomized controlled clinical trials of the use (or nonuse) of fetal fibronectin results in women with threatened preterm labor. The basic premise of fetal fibronectin testing in this setting is that, in women who present with threatened preterm labor, a negative fetal fibronectin could be used to reassure both providers and patients that a preterm birth was not imminent. This is based on the reported high negative predictive value of fetal fibronectin in this setting. Theoretically, this would lead to fewer admissions and fewer interventions (ie, tocolysis), while not increasing the rate of preterm birth. If this theory worked in practice, it would be an important advance in the care of women with threatened preterm labor.

But there were reasons to wonder whether it would work in everyday practice. One potential reason relates to which patients physicians actually would perform fetal fibronectin testing on and how that might impact the negative predictive values and therefore clinical management. In the observational study performed by Peaceman et al, of the women enrolled with threatened preterm labor, 73% of the women were having <4 contractions per hour, and 87% of the women were ≤1 cm dilated. In these women, only 3% went on to deliver within 1 week of testing. The negative predictive value was >99%. But two relevant questions are whether physicians would be testing this type of population and whether they would be willing to use the results of fetal fibronectin testing to guide clinical management.

A number of randomized clinical trials on this topic have been performed. The fundamental design of these studies is that women are assigned randomly to either physician knowledge of fetal fibronectin results or no physician knowledge of such results. Berghella and Saccone performed an elegant systematic review and meta-analysis and found the following results:

• •
  

  Six randomized controlled trials were included, with a total of 546 women.

  
  
• •
  

  Approximately 13% of women delivered within 1 week of enrollment.

  
  
• •
  

  Women who were assigned randomly to the knowledge of fetal fibronectin results did not have reduced rates of preterm birth at <37 weeks, <34 weeks, <32 weeks, or <28 weeks compared with the control group.

  
  
• •
  

  Women who were assigned randomly to knowledge of fetal fibronectin results had similar rates of hospitalization and the use of tocolytics and steroids compared with the control group.

  
  
• •
  

  Mean hospital costs were slightly higher in the knowledge of fetal fibronectin group.

  
  
• •
  

  No publication bias was identified, and statistical heterogeneity was low.

So it seems as if the initial promise for fetal fibronectin testing in women with threatened preterm labor (ie, avoidance of unnecessary interventions and hospital admissions at no cost to rates of preterm birth) has not been realized in the randomized controlled trials on this subject. In fact, hospital costs may be higher when fetal fibronectin results are used in clinical management. Based on the results of the individual studies and of this meta-analysis, the continued use of fetal fibronectin testing in women with threatened preterm labor cannot be justified.