There are many Fertility Apps that you can download to use on your smartphone and many are free. Used alone these Apps calculate your fertile time using a calendar method. These Apps rely on a traditional thinking about predicting the ovulation, which is based on the assumption that ovulation consistently occurs 14 days before the onset of your next period – so in the ‘middle of your cycle’ if you have a 28 day cycle. In fact, we now know that only a small percentage of women ovulate exactly 14 days before the onset of their period. So the calendar method is often really ineffective, and all these Apps are doing is keeping an electronic diary – more detailed and convenient than writing your cycle down on paper but not much more than that.
Some fertility Apps go a step further by taking into consideration how long your previous cycle lasted. The problem is because ovulation timing can vary even when you have consistent cycles, data from previous cycles don’t provide enough information to reliably predict individual fertility. Even though there is no doubt that tracking your fertility enables you to take some control and leads to a greater awareness of your cycle, to increase reliability and to be beneficial for conceiving you need to observe the physiological signs of fertility as well. This is where a fertility Monitor comes in.
Fertility Monitors used in conjunction with Apps offer greater reliability. As well as tracking your cycle, a Monitor gives you the ability to track your progesterone level by measuring temperature. There are two types of temperature which can be monitored: basal body temperature or core body temperature.
The most accurate method of tracking basal body temperature is by measuring in the mouth. A number of skin based monitors also exist but recent studies have shown this is not a particularly accurate method as it is subject to temperature disturbances due to environment and illness.
Studies have shown that the most accurate method of tracking temperature is to measure core body temperature in the rectum or vagina. The ability of core temperature, as opposed to oral or skin based temperature, to more accurately track the level of progesterone and to provide real time prediction of ovulation is confirmed by Coyne et al.