With most fertility apps, the main concern among users is simply, "Just how accurate is this thing?" Many apps claim to can monitor fertility via user imput, but women can still have negative experiences when trying to conceive. OvuSense, a new app, now uses women's own bodies to tell them when their most fertile.

OvuSense, developed by U.K.-based Fertility Focus, is a sensor that is placed in the vagina of the user overnight. Then, like downloading pictures, the women downloads her body temperature data into the app, giving them data that Fertility Focus claims is 99 percent accurate about an individual's fertility calendar.

Tested in more than 6,000 cases, OvuSense is able to provide a 24-hour advanced notice of ovulation with a clinically proven rate of 96 percent and a 99 percent accuracy of the exact date of ovulation. The sensor uses the women’s body temperature to determine the ovulation date instead of the usual urine test, which can give an incorrect result as often as one in five cycles.

“The key to OvuSense is that it monitors 'core temperature,' providing a direct indication of the [specific hormones] released during ovulation, but also allowing monitoring of levels in the rest of the cycle,” said Kate Davies, a fertility nurse. “That's helpful for all women, especially the 70 percent of women trying to conceive for more than six months who suffer with ovulatory issues."