Follow-up refers to the period after a trial participant is no longer receiving the study intervention or control, but the progress of participants continues to be followed. In perinatal trials we are often interested in longer term outcomes such as child development and survival free of disability. Sometimes a trial’s primary outcome can be considered as a form of follow up. For example, the primary outcome of the MAGENTA trial (ACTRN12611000491965) is death or cerebral palsy at 2 years of age. Follow up is used both to assess benefit and potential future harm. Participants in trials may be followed for many years e.g. the DOMInO trial (ACTRN12605000569606) has followed up children at 1.5, 3, 4, 5, 6 and 7 years and there has been a 30-year follow-up of children from the Liggins corticosteroid trial (Dalziel 2005). However it can be challenging to find participants as time passes. Follow-up is often very expensive and follow-up studies are often not funded or are under-funded (Doyle 2015). Increased access to routinely collected data sets and data linkage will help, but a need for direct participant follow-up will always remain.
Losses to follow-up at any stage of a trial are crucial considerations, as these may undermine the confidence we have in results where losses are high and/or unbalanced between intervention and control groups.
Dalziel SR, Walker NK, Parag V, et al. Cardiovascular risk factors after antenatal exposure to betamethasone: 30-year follow-up of a randomised controlled trial. Lancet. 2005; 365, 1856–1862.
Doyle LW, Clucas L, Roberts G, Davis N, Duff J, Callanan C et al. The cost of long-term follow-up of high-risk infants for research Studies: the cost of follow-up studies. Journal of Paediatrics and Child Health 2015;51:1012–6.