Background: Randomised controlled trials (RCTs) imply random allocation of participants to an intervention or a control group. When assessing risk of bias according to the Cochrane tool, the randomisation domain is crucial and may separate RCTs into low and high risk of bias.

Objectives: To compare meta-analyses of RCTs with low and high risk of bias in the randomisation domain.

Methods: A systematic review was performed within a health technology assessment (HTA) evaluating the effects of progesterone (Intervention) versus placebo (Comparison) in singleton pregnancies (Participants) regarding the Outcomes preterm birth (