of findings for the main comparison. Progesterone compared to placebo or no treatment for treating threatened miscarriage Progesterone compared to placebo or no treatment for treating threatened miscarriage Patient or population: women with threatened miscarriage Setting: two in high-income countries (Germany and Italy), four in upper-middle income countries (two in Iran, one in Malaysia and one in Turkey) and one in lower-income country (Jordan). All in hospitals (university or women's) or medical centres Intervention: progesterone Comparison: placebo or no treatment Anticipated absolute effects * (95% CI) Outcomes Risk with placebo or no treatment Risk with progesterone Relative effect (95% CI) № of participants (trials) Certainty of the evidence (GRADE) Comments Study population Miscarriage 242 per 1000 138 per 1000 (102 to 189) RR 0.64 (0.47 to 0.87) 696 (7 RCTs) ⊕⊕⊕⊝ Moderate 1 Study population Preterm birth 91 per 1000 84 per 1000 (49 to 142) RR 0.86 (0.52 to 1.44) 588 (5 RCTs) ⊕⊕⊝⊝ Low 1, 2 Study population Congential abnormalities 13 per 1000 9 per 1000 (1 to 62) RR 0.70 (0.10 to 4.82) 337 (2 RCTs) ⊕⊝⊝⊝ Very low 1, 2, 3 *The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; RCT: randomised controlled trial; RR: risk ratio GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect.