Randomised controlled trials (RCTs) that compared different tocolytic drugs (or compared with placebo or usual care) in women with a mean gestational age of between 28 and 33 weeks were eligible for inclusion. Studies where assigned treatments were not adequately concealed were excluded.
Interventions included different types of betamimetics, calcium-channel blockers, magnesium sulphate, nitrates, oxytocin receptor antagonists and prostaglandin inhibitors. Control treatments included placebo, usual care, bed rest and intravenous fluids. Outcomes of interest were rates of delayed delivery (at various time points), drug-related adverse events, neonatal survival and neonatal respiratory distress syndrome.
It was unclear how many reviewers were involved in selecting relevant abstracts, but two reviewers selected full articles for inclusion. Disagreements were resolved by consensus.