This study investigated if metabolomic profiling of culture media using near infrared (NIR) spectroscopy was related to live-birth rates after single-embryo transfer of frozen-thawed embryos. Analysis of culture media of frozen-thawed embryos was performed by NIR spectroscopy. A viability score was calculated using a predictive multivariate algorithm of fresh day-5 embryos with known pregnancy outcomes. This algorithm generated with fresh day-5 embryos could help to identify the live-birth group from the no live-birth group. Multivariable regression models that tested the predictive ability of the viability score for live birth showed an odds ratio in the crude analysis of 1.50 (P = 0.008), after adjustment for embryo morphology, 1.44 (P = 0.022), and after adjustment for all variables, 1.71 (P = 0.005); based on a 0.1 step increase in viability scores. In conclusion, higher viability scores resulted in higher live-birth rates. An algorithm generated from fresh embryos might be used to predict viability of frozen-thawed embryos. Frozen-thawed embryos have different metabolic activity which is related to implantation potential. Therefore, this method might be useful to select the best embryo for transfer within a group of embryos with similar morphology. In frozen-thawed embryo transfer (FET) cycles, usually more than one embryo is transferred. However, elective single embryo transfer (SET) might be effective in FET cycles when a good-quality embryo is selected. Viability assessment of frozen-thawed embryos is usually performed by morphological assessment. Although very helpful, morphological assessment remains subjective and can be unreliable in predicting embryo viability. New parameters to predict embryo viability, including non-invasive metabolomic profiling, have recently been studied. Metabolomics is the study of small-molecule metabolite byproducts left behind from cellular processes. By measuring byproducts of the embryonic metabolism in spent embryo culture media, a snapshot of the physiology of an embryo is obtained, which translates to viability. In this study, we investigated if metabolomic profiling by near infrared (NIR) spectroscopy was related to live-birth rates after SET of frozen-thawed embryos. Analysis of spent culture media of frozen-thawed embryos was performed by NIR spectroscopy and a viability score was calculated. The mean viability score from embryos with known implantation potential was significantly higher than the mean viability score of embryos which failed to implant: i.e. higher viability scores resulted in higher live-birth rates. Individual embryos showed a positive relationship between increased viability scores and increased live-birth rates. In other words, frozen-thawed embryos (of the same morphological grade) have different metabolic activity which is related to implantation potential. This indicates that the use of morphological and metabolomic criteria can both help with the decision of which embryo to transfer after thawing. © 2011 Elsevier Inc. All rights reserved.