Objective: To determine if vaginal ultrasound for cervical length measurement induces the release of vaginal fetal fibronectin (fFN), leading to a false-positive fFN test.
Methods: Participants included women with singleton pregnancies at 24-34 weeks' gestation who presented with uterine contractions without bleeding or membrane rupture. Women who had had intercourse or underwent pelvic examination less than 24 h previously were excluded. The first fFN test was followed immediately by vaginal ultrasonography with a transvaginal probe (three images per patient) and, thereafter, a second fFN test.
Results: The first fFN test was positive in three patients, and in all, the second, post-ultrasound, fFN test was also positive. In all women with a negative baseline fFN test (n = 25), the second, post-ultrasound, fFN test was also negative.
Conclusion: Vaginal ultrasound examination does not artificially change the fFN status. This is in contrast to common understanding and may permit the performance of ultrasound examination before fFN, which can be restricted to cases of short cervix.