Natural Cycles Ovulation Test measures the Luteinizing Hormone that occurs in a woman's body 1-2 days before ovulation and is a strong indication that ovulation is approaching. The tests are
What is LH?
LH stands for Luteinizing Hormone, which has its peak roughly 48 hours before ovulation. An increased LH is, therefore, a strong indication that ovulation may soon occur, but not a confirmation that ovulation has or will occur. As the peak is only for 48h maximum, this will not affect the app's fertility prognosis as the fertile window is six days in total. LH-tests are optional to do, and not a requirement for using Natural Cycles digital birth control.
Why should I do LH tests?
Measuring LH is great for narrowing down your ovulation, regardless of if you're a Prevent or a Plan user. Prevent users get roughly 5% more green days in a cycle with positive LH tests, and Plan users benefit from the extra accuracy in pinpointing ovulation and your most fertile days.
Remember that a positive LH test does not confirm that ovulation has, or will happen, but indicates that the body is initiating ovulation. A temperature rise must follow the positive ovulation test to confirm that ovulation has occurred. If you had a positive LH result but no placed ovulation yet, it's due to lack of data. It is important to then keep measuring properly during the coming days.
A negative LH-test does not confirm that you're not fertile, or that ovulation will not occur. This only means that no LH surge has been detected at the time you tested, so keep testing. You may need to test more often, 2-3 times a day in order to catch the surge. Ovulation will occur even if you've only gotten negative LH results, just remember to measure your temperature properly.
The combination of measuring body temperature and LH with Natural Cycles is a good combination for identifying the most fertile days of your cycle. Natural Cycles app also tells you which days you should take an LH test to not miss your LH peak. This usually means about 3-4 tests for a normal cycle.