Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); OBJECTIVE: To test the effectiveness of cervical pessary in addition to vaginal progesterone for the prevention of preterm birth in women with midpregnancy short cervixes. METHODS: We performed a multicenter, open-label, randomized controlled trial in 17 perinatal centers. Asymptomatic women with singleton or twin pregnancies and cervical len...