Study characteristics
A total of 20 studies participated in NMA comprising 4461 women (vaginal progesterone 1081, 17-OH progesterone 530, pessary 828, pessary plus progesterone 43, control group 1979). Twelve studies had progesterone as the main intervention: seven studies compared vaginal progesterone (varied between 90mg, 200mg, 400mg and 600mg) vs control group (placebo or standard treatment).30-36. Five studies compared intramuscular progesterone vs control group. The 17-OH progesterone dose varied between 250 to 1000mcg37-41.
Eight studies had cervical pessary as the main intervention: six studies compared pessary vs control group9,42-46, one study compared vaginal progesterone vs pessary47 and one study compared the combined intervention pessary + vaginal progesterone vs progesterone8. Table 1 shows the descriptive characteristics of the included studies. The full quality assessment result of the included studies using Rob2 is reported in Table S2.
Considering the study’s results including participants with a CL cut-off point (total sample or specific a subgroup), one study included women with CL ≤ 15mm30, three studies included CL ≤ 25mm41,43,44, one study included CL< 30mm36, two studies included CL ≤ 30mm8,45 , studies included CL <35mm9,40, one study included CL≤35mm46, one studiy included CL<38mm40 and eight studies included CL<40mm31-35,37-39.
Table 1 - Main characteristics of studies included in network meta-analysis