Fertility apps like Glow, Natural Cycles and Kindara are on the rise, and many women use them to avoid pregnancy without hormones or implants. But experts remain skeptical. Millions of women are turning to their smartphone to track their menstrual cycles. There are almost 100 apps to help them. Some are pretty simple, designed primarily to help women track their periods and predict ovulation. But others have more detailed features and bill themselves as an effective means of natural contraception. One app, Natural Cycles, used its own basal body thermometer and fertility prediction algorithm to become a certified method of contraception in Europe last year. Natural Cycles is currently awaiting a decision from the U.S. Food and Drug Administration on whether it can market the app as contraception in the U.S. In December, Natural Cycles released a study demonstrating that its app is 99 percent effective with perfect use and 93 percent effective with normal use, which is better than the pill. However, the app sparked criticism after 37 Swedish women got pregnant while using Natural Cycles as their primary form of birth control. » Subscribe to CNBC: http://cnb.cx/SubscribeCNBC About CNBC: From 'Wall Street' to 'Main Street' to award winning original documentaries and Reality TV series, CNBC has you covered. Experience special sneak peeks of your favorite shows, exclusive video and more. Connect with CNBC News Online Get the latest news: http://www.cnbc.com/ Find CNBC News on Facebook: http://cnb.cx/LikeCNBC Follow CNBC News on Twitter: http://cnb.cx/FollowCNBC Follow CNBC News on Google+: http://cnb.cx/PlusCNBC Follow CNBC News on Instagram: http://cnb.cx/InstagramCNBC Fertility Apps For Contraception Raise Skepticism | CNBC