Jarde A, et al. - The relative effects of different types and routes of administration of progesterone, cerclage and pessary at preventing preterm birth were determined in at-risk women overall and in specific populations. Researchers analyzed randomized trials of progesterone, cerclage or pessary for preventing preterm birth in at-risk singleton pregnancies searching Medline, EMBASE, CINAHL, Cochrane CENTRAL, and Web of Science up to January 1st, 2018. Outcomes support that only vaginal progesterone had consistent effectiveness for preventing preterm birth in singleton at-risk pregnancies overall and in those with a previous preterm birth.