Defining ‘usual care' in trials of complex interventions

Background Defining ‘usual care’ in studies of health services is challenging as it comprises a large variety of locally variable services. Building Blocks is trialling the Family Nurse Partnership Programme (FNP) in England. FNP is a complex intervention provided to first-time teenage mothers in the community setting. It was developed and previously trialled in the USA where support services are very different. To fully interpret trial results, particularly when making international comparisons, insight into the control condition is essential.