evidence: Background: The UK has one of the highest rates of teenage pregnancies in Western Europe. One-fifth of these are repeat pregnancies. Unintended conceptions can cause substantial emotional, psychological and educational harm to teenagers, often with enduring implications for life chances. Babies of teenage mothers have increased mortality and are at a significantly increased risk of poverty, educational underachievement and unemployment later in life, with associated costs to society. It is important to identify effective, cost-effective and acceptable interventions. [...] Conclusions: We found no evidence to indicate that existing interventions to reduce repeat teenage pregnancy were effective; however, subsequent births were reduced by home-based interventions. Qualitative and realist evidence helped to explain gaps in intervention design that should be addressed. More theory-based, rigorously evaluated programmes need to be developed to reduce repeat teenage pregnancy in the UK. [...] Intervention Now To Eliminate Repeat Unintended Pregnancy in Teenagers (INTERUPT): a systematic review of intervention effectiveness and cost-effectiveness, qualitative and realist synthesis of implementation factors and user engagement.BMJ Open. 2014 Apr 10;4(4):e004733. doi: 10.1136/bmjopen-2013-004733. BMJ Open. 2014. PMID: 24722200 Free PMC article. Review.