This paper presents an empirical evaluation of the COSMIC Function Points method (e.g., ISO 19761) through measuring the functional size of 33 prenatal mobile Personal Health Records (mPHRs) apps. This evaluation compares the functional size of each mobile app measured using the COSMIC method to the score of the app obtained in a previous evaluation that relied on functions extraction using a quality assessment questionnaire. It includes as well an investigation of the relationships between the functional sizes of these apps, their ratings in the apps stores, as well as the number of installs. As results, it was noticed that there is a considerable shift between the rankings of the functional sizes and the functionality scores obtained in the opinion-based questionnaire, for most of the apps assessed. Moreover, the study of the relationship between the functional sizes and the ratings, as well as the number of installs indicated that these variables are not linked, since they are impacted by external factors. The findings support the use of the COSMIC method for these apps in regard to measuring the functional size for further updates or improvements, which can also help developers to have an overview about the existing apps on the market and compare between them. Moreover, COSMIC is more effective since it covers all the features and functionalities of prenatal mPHRs.