Comparison 1. Threatened miscarriage: Vaginal micronized progesterone versus placebo.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1.1 Live birth	2	4090	Risk Ratio (M‐H, Fixed, 95% CI)	1.03 [1.00, 1.07]
1.2 Miscarriage (defined as delivery before 24 weeks of gestation)	2	4090	Risk Ratio (M‐H, Fixed, 95% CI)	0.90 [0.80, 1.01]
1.3 Preterm birth (defined as birth before 37 weeks of gestation)	2	3154	Risk Ratio (M‐H, Fixed, 95% CI)	1.08 [0.92, 1.27]
1.4 Stillbirth	1	4038	Risk Ratio (M‐H, Fixed, 95% CI)	0.83 [0.25, 2.71]
1.5 Ectopic pregnancy	1	4038	Risk Ratio (M‐H, Fixed, 95% CI)	0.20 [0.01, 4.14]
1.6 Congenital abnormalities	1	3085	Risk Ratio (M‐H, Fixed, 95% CI)	1.00 [0.68, 1.46]
1.7 Adverse drug events	1	4038	Risk Ratio (M‐H, Fixed, 95% CI)	1.07 [0.81, 1.39]
1.8 Live birth (subgrouped by no previous miscarriages and one or more previous miscarriages)	2		Risk Ratio (M‐H, Fixed, 95% CI)	Subtotals only
1.8.1 No previous miscarriages and early pregnancy bleeding	2	2261	Risk Ratio (M‐H, Fixed, 95% CI)	0.99 [0.95, 1.04]
1.8.2 One or more previous miscarriages and early pregnancy bleeding	2	1829	Risk Ratio (M‐H, Fixed, 95% CI)	1.08 [1.02, 1.14]
1.9 Live birth (subgrouped by maternal age)	1		Risk Ratio (M‐H, Fixed, 95% CI)	Subtotals only
1.9.1 Maternal age < 35 years	1	3113	Risk Ratio (M‐H, Fixed, 95% CI)	1.03 [0.99, 1.07]
1.9.2 Maternal age ≥ 35 years	1	925	Risk Ratio (M‐H, Fixed, 95% CI)	1.04 [0.95, 1.13]