2.1.2 Inclusion criteria
Study type: RCTs and non-RCTs (including cohort studies).
Study subjects: pregnant women with a short cervical length (CL) <25mm in the second trimester who received cervical pessary or transvaginal cervical cerclage to prevent spontaneous preterm birth.
Interventions: cervical pessary of any type in the trial group, and transvaginal cervical cerclage of any technique in the control group.
Outcome measures: 1) abortion rate before 28 weeks; 2) premature birth rate before 32 weeks; 3) premature birth rate before 34 weeks; 4) premature birth rate before 37 weeks; 5) mean gestational weeks at delivery; 6) incidence of preterm premature rupture of the membranes (PPROM); 7) neonatal survival rate; 8) neonatal birth weight; and 9) cesarean section rate.