Background Assisted reproductive technologies (ARTs) are considered to be physically and mentally stressful. During their treatment trajectory, couples express high information and communication needs. They appreciate using the internet to obtain fertility-related information. In a previous study, we developed myFertiCare, an eHealth tool providing personalized information and interactive functionalities for infertile couples in order to improve patient-centered care. The app has already been successful in qualitative evaluations of usability. Objective The aim of the current study is to quantitatively evaluate the implementation of myFertiCare by using the human, organizational, and technology–fit (HOT-fit) framework and to study the effects of using myFertiCare on couples’ knowledge about infertility, their experience of the burden of infertility, and their experience of patient-centered care. With these results, implementation can be further improved, and patient-centered care can be enhanced. Methods A quantitative study was performed based on the HOT-fit framework using validated questionnaires focusing on the human, organizational, and technology domains. Questions were added on the effect of using myFertiCare on couples’ knowledge about infertility and treatment. Questions regarding the burden of infertility, the burden of infertility treatment, and the experience of patient-centeredness were based on the main items of the validated fertility quality of life (FertiQoL) and Patient-Centredness Questionnaire–Infertility questionnaires, respectively. Also, nonusers of the app were included to explore motivations for not using the app and identify opportunities for improvement. Finally, user data were analyzed to provide insight into multiple variables concerning app use. Results In the human and technology domains, myFertiCare showed good system usability, high user satisfaction, and high information and interface quality. In the organizational domain, implementation was considered to be sufficient by both patients and staff. Use of the app increased knowledge about the treatment, improved coping with the treatment, and enhanced the experience of patient-centeredness. User data showed that women were the main app users and that use of the app gradually declined during the treatment trajectory. Conclusions A multi-faceted online app, myFertiCare, has been successfully evaluated quantitatively for implementation by using the HOT-fit framework. Use of the app increased knowledge about the treatment, improved coping with the treatment, and enhanced the experience of patient-centeredness. App use could be improved by creating more publicity. By providing myFertiCare, professionals in fertility care are supported in guiding patients through their treatment trajectory and in delivering patient-centered care.