Cervical insufficiency (CI), responsible for 8% of preterm births (PB), is used to describe painless cervical dilation leading to recurrent second-trimester pregnancy losses/births of otherwise normal pregnancies. Structural weakness of cervical tissue was thought to cause or contribute to these adverse outcomes. The term has also been applied to women with one or two such losses/births or at risk for second-trimester pregnancy loss/birth. Cervical pessary and cervical cerclage are both considered as preventive treatments in women at risk for PB. This study aims to demonstrate that the cervical pessary could reduce the preterm birth rate before 37 weeks of gestation in women with prior PB due to cervical insufficiency or in women with prior PB and a short cervix in the current pregnancy.