Compositions comprising selenium (e.g., organic selenium (e.g., selenized yeast (e.g., SEL-PLEX))) and methods of using the same (e.g., as a therapeutic and/or prophylactic treatment) are provided. For example, compositions comprising selenium (e.g., organic selenium (e.g., selenized yeast (e.g., SEL-PLEX))) and methods of using the same are provided for treating and/or preventing one or more conditions (e.g., problems) disorders, and/or diseases related to establishing and/or maintaining a pregnancy. Compositions and methods of the invention find use in, among other things, research and clinical (e.g., preventative and therapeutic) applications.