EVALUATING THE RISK OF PRETERM DELIVERY - A COMPARISON OF FETAL FIBRONECTIN AND TRANSVAGINAL ULTRASONOGRAPHIC MEASUREMENT OF CERVICAL LENGTH

OBJECTIVE: Our purpose was to compare the predictive values for preter m delivery of fetal fibronectin and cervical length measured by transv aginal ultrasonography and to determine whether performing both tests improves their separate predictive values. STUDY DESIGN: This prospect ive blinded study performed both tests on 76 patients hospitalized wit h signs of premature labor between 24 and 34 weeks of gestation. The o utcome measure was delivery before 37 weeks' gestation. RESULTS: The r ate of preterm birth was 26.3% (20/76). The predictive values of fetal fibronectin and of a cervical length of less than or equal to 26 mm, considered separately, were approximately equal, and the negative pred ictive value of each was excellent (86.6% and 89.1%, respectively). Th is value improved slightly when positive fetal fibronectin, a cervical length less than or equal to 26 mm, or both defined abnormality (nega tive predictive value 94.4%). The positive predictive values, although less helpful, were still useful (45.2% and 50.0%, respectively). Comb ining both indicators did not noticeably improve the positive predicti ve value (52.4%). The risk of preterm delivery for a patient with a po sitive fetal fibronectin level and a short cervix was high (odds ratio 13.9, 95% confidence interval 3.7 to 52.2). CONCLUSION: Fetal fibrone ctin and cervical length are approximately equivalent in their ability to distinguish between patients at high and low risk for preterm deli very. For physicians equipped to perform transvaginal ultrasonography, however, the additional information about the fibronectin level provi des only slight benefits.