You can use the apps on from phone for seemingly just about anything—but you might want to think again when using them to avoid pregnancy.

A study, led by Marguerite Duane, MD, MHA, FAAFP, adjunct associate professor at Georgetown University School of Medicine and executive director of Fertility Appreciation Collaborative to Teach the Science (FACTS), found that most fertility awareness apps do nothing to help women avoid pregnancy. Some even include a disclaimer discouraging use for avoiding pregnancy.

"Smartphone apps are increasing in popularity because more and more women are interested in using natural or fertility awareness-based methods of family planning because they want to feel empowered with greater knowledge of their bodies," said Duane. "The effectiveness of fertility awareness based methods (FABMs) depends on women observing and recording fertility biomarkers and following evidence-based guidelines. Apps offer a convenient way to track fertility biomarkers, but only some employ evidence-based FABMs."

The study started by analyzing 100 different fertility apps but that number quickly dropped to 40 when the excluded apps had included a disclaimer stated to not use the app for avoiding pregnancy or did not claim to employ an evidence-based FABM.

The remaining 40 apps were then tested for accuracy using a five-point scale for 10 different criteria. "Of those reviewed, 30 apps predict days of fertility for the user and 10 do not,” wrote researchers. “Only six apps had either a perfect score on accuracy or no false negatives.”

"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 Duane.