Employers are increasingly contracting with firms that use big data to predict and promote employee health. By aggregating claims data, browser searches, and demographic information, these firms can foresee whether employees are at risk for health issues—and their associated costs—and target preventive resources accordingly. However, a recent report1 indicates that this analytic capability is being extended to predict not only diabetes or the need for back surgery but also whether an employee is or is considering becoming pregnant. This trend raises troubling questions about the appropriate limits of wellness program analytics. When is an employer’s use of big data a legitimate prevention strategy, and when is it an impermissible intrusion into employee privacy?