Definition and Diagnosis of Preterm Labor

Abstract

Preterm birth is the leading cause of neonatal mortality and morbidity, as well as the most common reason for antenatal maternal hospitalization. Preterm labor is defined as regular uterine contractions associated with cervical changes (cervical dilatation ≥2 cm and effacement) that start before 37 weeks of gestation. However, the diagnosis of threatened preterm labor is imprecise to identify women who will give birth preterm infants in near future. In the last few decades, more subjective parameters are used, which include cervical length measured by transvaginal ultrasonography, fetal fibronectin concentrations of the cervicovaginal secretions, and the combination of the two tests. Prospective studies show that shorter cervical length (15–30 mm or less) is significantly associated with spontaneous preterm delivery. Systematic reviews show that fetal fibronectin measurement combined with shorter cervical length has a high negative predictive value (>98%) for delivery within 7 days but a low positive predictive value (30–50%). The prenatal caregivers should take full advantage of the high negative predictive value of the combined test for women with threatened preterm birth.