Preterm birth is the leading cause of perinatal morbidity and mortality in developed nations. The heterogeneous causes of spontaneous preterm birth make prediction and prevention difficult. The primary importance of transvaginal cervical sonography and cervicovaginal fetal fibronectin lies in their high negative predictive values in assessing risk for preterm birth. Cervical length may be useful in identifying women who are candidates for cervical cerclage or progesterone therapy for preterm birth prevention. Together, cervical length and fibronectin can be used in the triaging of women symptomatic for preterm labor.