Do fertility apps accurately calculate the female fertility window?

​Most Fertility Apps Miscalculate the Fertile Window
Fertility websites and smartphone apps vary in how they calculate a woman's fertile window, and many get it wrong, according to a new study. For example, 78.8% of apps and 75.0% of websites included days after ovulation as part of the fertile window, even though conception is unlikely to occur during that part of a woman's cycle.
"Although for this study we assumed a 'perfect cycle,' it can be implied that with the inherent variation in actual cycles, the predicted fertile windows may be even more inaccurate," Robert Setton, MD, from the Department of Obstetrics and Gynaecology at Weill Cornell Medical College in New York City, and colleagues write in an article published online June 6 and in the July issue of Obstetrics & Gynaecology.
The investigators selected the top most popular free apps on both Android and iOS platforms (33 apps total), as well as the top 20 websites, using a search for "ovulation calendar" or "fertility calendar." They logged a menstrual period beginning on January 1. With a 28-day cycle, the investigators calculated that ovulation should occur on January 15, with a fertile window from January 10 to January 15. That estimate comes from what they describe as the "gold standard" for calculating a fertile window, as described in the New England Journal of Medicine in 1995 by Allen Wilcox and colleagues.
Only one website and three apps predicted that same fertile window.
Some gave drastically different results, with the fertility window starting as early as day 4 in some calendars, and some going as late as day 21.
The websites and apps also varied in the length of the fertile window, with the shortest giving a 4-day window and the longest, 12 days. Among all of the websites and apps, only day 14 was included in every fertile window. However, in total, 75% of the fertile days predicted by apps fall in the "gold standard" fertile window, as did 74% of the fertile days predicted by the apps.
Not all calendars identified a day of ovulation, but the ones that did were usually accurate: 80.0% (95% confidence interval [CI], 0.44 - 0.98) of websites and 86.9% (95% CI, 0.66 - 0.97) of apps selected day 15. Dr Setton and colleagues did not publish the names of the websites or apps that were surveyed.
"The research by Dr. Setton demonstrates that web-based and app-based resources intended to help couples identify the fertile window are, generally, inaccurate," Hal C. Lawrence, MD, chief executive officer of the American College of Obstetricians and Gynaecologists said in a media statement. "Although Dr. Setton did not study the clinical implications of this, it's important for women to know that reliance on these digital platforms may not be effective for them."
Because couples sometimes abstain from sex before the onset of the fertile window, an app that gives the start as being too early may not help a couple maximize their chances of conceiving, Dr Setton and colleagues write. "Practitioners should be aware that most of these [apps and websites] give patients inaccurate information, and patients should be counselled accordingly."
 (The article was published at the medscape.com.)