Randomised trials are the gold standard for assessing which new treatments, including those in early life, are the most effective for improving life-long health. To maximise the potential benefits of such trials, and assess long-term benefits and risks, detailed follow-up of participants is required over many years, but this is difficult, expensive, and often not feasible. This programme will undertake crucial, long-term follow-up of participants in six key randomised trials involving mothers and babies. At the same time, we will develop new assessment approaches for use in multiple future studies, evaluate the use of nationally collected datasets for this purpose, and engage with consumers, including Māori, to understand their outcome priorities. This programme will provide critical new information to evaluate efficiently current new treatments and build a skilled workforce. It will also build New Zealand capacity to evaluate early life research and policy changes in the future.