['Currently, morphological criteria are used to select embryos for transfer in in vitro fertilization (IVF)-embryo transfer. However, the implantation rate is only about 30%, indicating a need for a more efficient method of selecting high-quality embryos. This study investigated the relationship between medium ammonium concentration and IVF implantation rates and evaluated the possibility of using ammonium concentration to provide an objective, noninvasive, and simple means of assessment of embryo viability.', 'On day 3 after fertilization, we sampled the spent medium bathing embryos obtained from patients undergoing IVF or intracytoplasmic sperm injection (ICSI) at the Reproductive Medical Center of Sun Yat-sen Memorial Hospital, between September 2010 and January 2012. The concentration of ammonium was determined using a dry chemistry system.', 'The ammonium concentration increased significantly during the period of culture of all embryos, but the increase was significantly greater in the group that, subsequently, did not achieve pregnancy (P < .001). An receiver-operating characteristic (ROC) curve indicated that ammonium concentration was highly predictive of embryo implantation failure (area under ROC curve = 0.838). Failure to achieve implantation had a predictive sensitivity of 71% and specificity of 79.6%. The accuracy of prediction of successful or failed implantation was 75.4%. In both IVF and ICSI, the embryo implantation rate decreased significantly as the medium ammonium concentration increased (P < .05).'] Does ammonium concentration of spent medium provide a noninvasive assessment of embryonic developmental potential in IVF?