This is one of a series of occasional articles that highlight areas of practice where management lacks convincing supporting evidence. The series advisers are Rubin Minhas, clinical director, BMJ Evidence Centre, and David Tovey, editor in chief, the Cochrane Library. This paper is based on a research priority identified and commissioned by the National Institute for Health Research’s Health Technology Assessment programme on an important clinical uncertainty. To suggest a topic for this series, please email us at uncertainties@ bmj. com.

Miscarriage is the commonest complication of pregnancy, occuring in one in six clinically recognised pregnancies. 1 Recurrent miscarriage is the loss of three or more consecutive pregnancies. Women with recurrent miscarriage (in contrast to women with sporadic miscarriage) tend to lose genetically normal pregnancies. 1 After comprehensive investigation, a cause for recurrent miscarriage is identified in less than half of couples. 1 Most couples are therefore labelled as having unexplained recurrent miscarriage.