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BACKGROUND: The E-Freeze trial is a multi-centre randomised controlled trial of fresh versus frozen embryo transfer for women undergoing in vitro fertilisation. This paper describes the statistical analysis plan for the E-Freeze trial. METHODS AND DESIGN: E-Freeze is a two-arm parallel-group, multi-centre, individually randomised controlled trial to determine if a policy of freezing embryos, followed by thawed frozen embryo transfer, results in a higher healthy baby rate when compared with the current policy of transferring fresh embryos. Couples undergoing their first, second or third cycle of in vitro fertilisation at fertility centres in the UK were randomised to either fresh or frozen embryo transfer. The primary outcome is a healthy baby, defined as a live singleton baby born at term with an appropriate weight for gestation. This paper describes the statistical analysis plan for the trial, including the analysis principles, definitions of outcomes, methods for primary analysis, pre-specified subgroup analysis and sensitivity analysis. This plan was finalised prior to completion of recruitment to the trial. TRIAL REGISTRATION: ISRCTN registry: ISRCTN61225414 . Registered on 29 December 2015.

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Assisted conception, Complier average causal effect, Elective freezing, Fertility, Fresh embryo transfer, Frozen thawed embryo transfer, IVF, OHSS, Randomised controlled trial, Receptivity, Statistical analysis plan