Why Were the Results of Randomized Trials on the Clinical Utility of Fetal Fibronectin Negative? A Systematic Review of Their Study Designs - Vis, Jolande Y; Wilms, Femke F; Oudijk, Martijn A; Bossuyt, Patrick M.M.; van der Post, Joris A.M.; Grobman, William A; Mol, Ben Willem J (American Journal of Perinatology, 2011)