Abstract: Single embryo transfer（SET） is a useful method to reduce multiple pregnancies （MP） rate， the optimal embryo selection is the key factor to maintain success rates with SET. Presently，morphology and cleavage rate used in many centers remain the mainstay of embryo assessment， but they have a limited predictive value for assessing viability and ongoing pregnancy. Recent studys indicate that the metabolism analysis combinded with the current methods of embryo assessment would be more effective to select high-quailty embryos， increase the rate of pregnancy as well as reduce multiple pregnancies （MP） rate.

Key words: Single embryo transfer, Embryonic development, Culture in vitro, Assessment