Perinatal morbidity and mortality increase in proportion to the time from waited date of labor to birth. A test helping to predict pregnancies is required, which also helps to predict pregnancies that will progress more than 41 weeks.To determine the usefulness of fetal fibronectin in vaginal secretions to predict pregnancies that will progress 41 weeks or more.A cohort and descriptive study was done in which 144 women with a pregnancy of 40 weeks or more were included. Fetal fibronectin was detected in cervix-vaginal secretions and time from the sample obtaining to birth was estimated.Seventy patients with positive fibronectin were recorded; 92% had labor in the following seven days from the sample obtaining (interval mean: 3.1 days). The remaining patients (n = 44) resulted with negative fibronectin; only 37.5% had spontaneous labor, but none of them during the first four days from the sample obtaining (mean: 7.9 days).Absence of fetal fibronectin in vaginal secretions is a good prognostic marker to identify patients who will achieve a pregnancy of 41 weeks or more (sensitivity of 70% and specificity of 84%; positive and negative predictive value of 75% and 80.7%, respectively, and relative risk of 10, CI 95%, 5.7-14.3). This method is useful to prevent perinatal complications inherent to the pregnancy of 41 weeks or more.