STUDY QUESTION: What is the relationship between the rate of elective single-embryo transfer (eSET) and couples' exposure to different elements of a multifaceted implementation strategy? SUMMARY ANSWER: Additional elements in a multifaceted implementation strategy do not result in an increased eSET rate. WHAT IS KNOWN ALREADY: A multifaceted eSET implementation strategy with four different elements is effective in increasing the eSET rate by 11%. It is unclear whether every strategy element contributes equally to the strategy's effectiveness. STUDY DESIGN AND SIZE: An observational study was performed among 222 subfertile couples included in a previously performed randomized controlled trial. PARTICIPANTS, SETTINGS AND METHODS: Of the 222 subfertile couples included, 109 couples received the implementation strategy and 113 couples received standard IVF care. A multivariate regression analysis assessed the effectiveness of four different strategy elements on the decision about the number embryos to be transferred. Questionnaires evaluated the experiences of couples with the different elements. MAIN RESULTS AND ROLE OF CHANCE: Of the couples who received the implementation strategy, almost 50% (52/109) were exposed to all the four elements of the strategy. The remaining 57 couples who received two or three elements of the strategy could be divided into two further classes of exposure. Our analysis demonstrated that additional elements do not result in an increased eSET rate. In addition to the physician's advice, couples rated a decision aid and a counselling session as more important for their decision to transfer one or two embryos, compared with a phone call and a reimbursement offer (P < 0.001). LIMITATIONS AND REASONS FOR CAUTION: The differences in eSET rate between exposure groups failed to reach significance, probably because of the small numbers of couples in each exposure group. WIDER IMPLICATIONS OF THE FINDINGS: Adding more elements to an implementation strategy does not always result in an increased effectiveness, which is in concordance with recent literature. This in-depth evaluation of a multifaceted intervention strategy could therefore help to modify strategies, by making them more effective and less expensive.