Using a fertility app on your smartphone to plan or prevent a pregnancy might not be such a good idea, warns a new study published in the Journal of the American Board of Family Medicine. The recent review of nearly 100 family planning apps found that many don’t follow evidence-based medical guidelines and may offer imprecise information to women aspiring (or not aspiring) to be mothers, ReliaWire reports.

For the study, researchers at the Georgetown University School of Medicine examined the efficacy of a wide array of smartphone apps promising to help women track the days they were most fertile using common biomarkers. Scientists reviewed popular menstruation-focused apps, such as Lady Cycle, Period Log and Pink Pad Pro, as well as those based on ovulation, including Knowhen, Cyclendar and Fertility Clock.

Of more than 100 pregnancy and period apps reviewed, researchers said only six nailed a perfect score on accuracy or no false negatives (days of fertility classified and infertile).

Study authors noted that as more women become interested in using all-natural birth control or pregnancy-planning techniques, smartphone apps like these have been increasing in popularity during the last few years.

“When learning how to track your fertility signs, we recommend that women first receive instruction from a trained educator and then look for an app that scored 4 or more on mean accuracy and authority in our review,” said Marguerite Duane, MD, an adjunct associate professor at Georgetown University School of Medicine and executive director of Fertility Appreciation Collaborative to Teach the Science (FACTS), the study’s lead author.

For more information about which family planning apps worked best, visit the FACTS website. To learn more about how to track your fertility and ovulation patterns on your own, click here.