Background Miscarriage, defined as the spontaneous loss of a pregnancy before 24 weeks’ gestation, is common with approximately 25% of women experiencing a miscarriage in their lifetime, and 15% to 20% of pregnancies ending in a miscarriage. Progesterone has an important role in maintaining a pregnancy, and supplementation with different progestogens in early pregnancy has been attempted to rescue a pregnancy in women with early pregnancy bleeding (threatened miscarriage), and to prevent miscarriages in asymptomatic women who have a history of three or more previous miscarriages (recurrent miscarriage). Objectives To estimate the relative effectiveness and safety profiles for the different progestogen treatments for threatened and recurrent miscarriage, and provide rankings of the available treatments according to their effectiveness, safety, and side-effect profile. Search methods We searched the following databases up to 15 December 2020: Cochrane Central Register of Controlled Trials, Ovid MEDLINE(R), ClinicalTrials.gov and the WHO International Clinical Trials Registry Platform (ICTRP), and reference lists of retrieved studies. Selection criteria We included all randomised controlled trials assessing the effectiveness or safety of progestogen treatment for the prevention of miscarriage. Cluster-randomised trials were eligible for inclusion. Randomised trials published only as abstracts were eligible if sufficient information could be retrieved. We excluded quasi- and non-randomised trials. Data collection and analysis At least two review authors independently assessed the trials for inclusion and risk of bias, extracted data and checked them for accuracy. We performed pairwise meta-analyses and indirect comparisons, where possible, to determine the relative effects of all available treatments, but due to the limited number of included studies only direct or indirect comparisons were possible. We estimated the relative effects for the primary outcome of live birth and the secondary outcomes including miscarriage (< 24 weeks of gestation), preterm birth (< 37 weeks of gestation), stillbirth, ectopic pregnancy, congenital abnormalities, and adverse drug events. Relative effects for all outcomes are reported separately by the type of miscarriage (threatened and recurrent miscarriage). We used the GRADE approach to assess the certainty of evidence.