Objective: Our purpose was to determine whether the presence of fetal fibronectin in cervicovaginal secretions of patients undergoing induction of labor reflected the cervical state and ultimately the ease of induction of labor.
Study design: A prospective observational study of 103 patients undergoing induction of labor at term was conducted at Liverpool Maternity Hospital, a large university teaching hospital. We studied the women after 37 completed weeks of pregnancy. A Dacron (Adeza Biomedical, Sunnyvale, Calif.) polyester swab specimen was first taken from the endocervix for assessment of the presence of the fetal fibronectin. The cervix was then assessed by digital vaginal examination and scored with a modified Bishop's score. The fetal fibronectin swab was processed at the bedside with a membrane immunoassay kit specific for fetal fibronectin. A score was ascribed depending on the strength of the fibronectin reaction determined by the intensity of the color change on the plate, the presence of fetal fibronectin resulting in a score of 1 to 4. The patient was subsequently managed according to the standard induction protocol of the unit. The clinicians involved in the patient's care were blind to the result of the fetal fibronectin swab.
Results: There was a good correlation between the modified Bishop's score and the fetal fibronectin score (r = 0.58, p < 0.001). To predict a latent phase of < 8 hours, a fetal fibronectin score of 3 or 4 has a sensitivity of 73% with a specificity of 83% and a modified Bishop score of > or = 4 has a sensitivity of 75% and a specificity of 73%. For delivery within 12 hours of induction of labor a fetal fibronectin score of > or = 3 has a sensitivity of 61% and specificity of 83% compared with the modified Bishop score of > or = 4, which has a sensitivity of 76% and a specificity of 72.5%.
Conclusions: The fetal fibronectin score is as good as the modified Bishop score as an index of the ease with which induction of labor may be performed. This would imply that it also reflects the proximity of the onset of labor. The presence of fetal fibronectin cervicovaginal secretions is therefore a marker of the changes in the cervix and membranes that precede labor regardless of the gestational age.