The modes of expression in assisted reproductive techniques are numerous. The delivery rate per started cycle must include the deliveries issued of thawed embryos transfer. The birth rates per patient are a different modality of great interest for the crude as well as the actuarial cumulative delivery rates. But all these data should be interpreted within their context: selection of patients or health policy. The disparity of expression of results comes from the function of these results. Scientific analysis, public health, monitoring quality and prognostic value are the four main purposes justifying differentiated expression modes.
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