What is the most relevant standard of success in assisted reproduction? Is besst (birth emphasizing a successful singleton at term) truly the best?

There much variability and no consensus on the definition of the most relevant outcome parameter after assisted reproduction technology (ART). Descriptive reports, such as annual statistics from national registries on the success of ART programmes, should present treatment success in terms of live birth per ovarian stimulation started, as this is the most relevant information for patients and doctors alike. Addressing concerns about the high rate of multiple pregnancies, rescaling the outcome of ART in large programmes and national audits to the singleton, live birth, might trigger a global change of attitude towards elective single embryo transfer in addition to any legal restrictions imposed. For clinical studies, the outcome measure will depend on the hypothesis tested, and investigators should remain free to choose the appropriate primary outcome measure.