Using one of those many smartphone apps to track your fertility? Don’t bother, they’re almost certainly worthless, a new study has found.

Researchers reviewed around 100 smartphone fertility applications used in the United States and discovered that most of the apps didn’t assist at all either in achieving pregnancy or in preventing it, according to a Georgetown University statement.

That’s unfortunate, because people are increasingly relying on apps to track their fertility.

The researchers found that at least 55 percent of the apps had a disclaimer stating that they weren’t meant to be used to avoid pregnancy, but that also means a large minority did not.

Typically, the fertility applications attempt to track a woman’s menstrual cycle and then note which days they are likely to be ovulating and therefore would be the best time to try to get pregnant — or avoid unprotected sex if they didn’t want a pregnancy. The smartphone apps work by monitoring the basal body temperature of the user, which is when the body is at rest.

“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,” says DMarguerite Duane, MD, MHA, FAAFP, adjunct associate professor at Georgetown University School of Medicine. “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.”