Objective: To compare the health and economic impacts of implementing efficacious treatment interventions with maintaining standard practice in maternal and perinatal health care. Design and setting: We identified randomised clinical trials (RCTs) in the Perinatal Society of Australia and New Zealand trials database that commenced recruitment during 2008 and had completed recruitment by 2015. Data from clinical trial registries and publications were collated to calculate the potential cost savings achievable by implementing efficacious treatment interventions. Main outcome measure: Projected net cost savings over 5 years. Results: Twenty-three eligible RCTs covering a range of behavioural and clinical interventions were identified, of which six reported interventions superior to standard practice (four trials) or placebo (two). The outcomes (but not the costs) of 17 trials were excluded from analysis (no difference between intervention and comparator groups in seven trials, recruitment problems in six, findings not yet published in four). The total funding amount for the 23 trials was $20.3 million; the potential cost savings over 5 years if the findings of the six trials reporting superior interventions were implemented was estimated to be $26.3 million if 10% of the eligible populations received the effective interventions, and $262.8 million with 100% implementation. Conclusions: Our retrospective analysis highlights the value of research in perinatal care and the importance of implementing positive findings for realising its value. Future trials in maternal and perinatal health care may provide significant returns on investment by informing clinical practice, improving patient outcomes and reducing health care costs.