When I first decided to write my book back in the Stone Ages, the internet had yet to take over our lives. So at that time, the thing that kept me up nights was my concern that women could misunderstand concepts in the book, leading to either unplanned pregnancies, or not conceiving when desperately wanting to.

Today, those fears seem almost naïve compared to a much bigger concern: the pervasiveness of scores of Fertility Awareness apps that claim to be able to predict a woman’s fertility based on nothing more than inputting the first day of a period, or occasionally basal temperatures.

In fact, the internet is flooded with these beautifully designed apps with gorgeous colors devised to monitor a woman’s menstrual cycle. But beware! Those data alone are not enough to be able to determine a woman’s fertile phase, and are often nothing more than a high-tech version of the antiquated Rhythm Method.

In order to judge whether an app is reliable, at a minimum, it should allow you to input your cervical fluid in addition to basal body temperature, as well as other secondary fertility signs such as ovulatory pain. Those that only include temps cannot indicate when ovulation is about to occur, but only confirm if ovulation has already happened. To know on a daily basis whether or not you are fertile, you need to observe and record your cervical fluid, which is critical for both contraceptors and pregnancy achievers.

Regardless, I encourage you to thoroughly read the latest edition of my book, Taking Charge of Your Fertility (2015) or better yet, also take a class in the Fertility Awareness Method before using one of these apps, because they alone can’t possibly provide you with the instruction and personal counseling necessary to be able to understand how to rely on your primary fertility signs. And as proud as I am of my own app, OvaGraph, even I admit that apps should be used only as a convenient way to always have your charts with you, and even to share them with a clinician or others. However, they are certainly not a replacement for proper education about your body, fertility and cycles.