While measuring LH is optional, it can boost the accuracy of your ovulation detection and fertility predictions.
For NC° Birth Control users, measuring LH may result in more green days, however, LH tests don’t affect the effectiveness of Natural Cycles as birth control.
NC° Plan users benefit from the extra accuracy in pinpointing their most fertile days.
How does logging a positive LH test influence ovulation detection?
For that reason, when you log a positive LH test in the app, your ovulation prediction will adapt accordingly.
As the surge only lasts for a brief two day period at most, and doesn’t always trigger ovulation within the following few days, the detected LH peak needs to be followed by elevated temperatures to confirm that ovulation did take place.
Once the algorithm has detected elevated temperatures it will confirm ovulation accordingly and it will take into account the positive LH test, along with the temperature curve, to pinpoint the most likely day. If you logged a positive LH test and a temperature rise is detected in the following days, you may get green days sooner than if you had not logged a positive LH test.
That being said, as the temperature is the main factor that the algorithm uses to detect ovulation, it’s important to remember that the algorithm will always prioritize temperature data over LH data, particularly if these give conflicting information. This means that if you logged a positive LH test on Cycle Day 10 (CD10) and your temperature only increased from CD18, the algorithm might place ovulation around CD18, even if that was more than two days after the logged positive LH test.
Why does Natural Cycles prioritize temperature data over LH data?
A positive LH test indicates that the body is initiating ovulation. It is, however, important to keep in mind that it doesn’t confirm that ovulation has, or will, happen. A temperature rise must follow the positive ovulation test for the Natural Cycles algorithm to confirm that ovulation has occurred.
A negative LH test doesn’t mean that you're not fertile, or that ovulation will not occur. This only means that no LH surge was detected at the time you tested, so you can keep testing if you want.
Because LH tests can only indicate that ovulation might soon happen, Natural Cycles prioritizes temperature data over LH data, and it’s important to keep on logging temperature data regularly in addition to the optional LH tests.
For those with conditions such as PCOS where "false" LH peaks can occur (where an LH rise occurs but the egg is not released, so no progesterone is released and no temperature rise happens, which Natural Cycles identifies), LH testing is not recommended.
The algorithm may prioritize LH data over temperature data if you’ve missed a few days of temperature data around the time ovulation happened, or if your temperatures were fluctuating around that time. If the algorithm cannot fully rely on the temperature data for any reason, it will give more importance to the LH test results as long as an overall temperature shift was detected. (Note: missing a few days of temperature is not the same as not adding any temperature data at all — head over to the next section for more information).
Can the algorithm detect ovulation if I only log LH tests and no temperature data?
If you never log any temperature data, the algorithm will not be able to identify your fertile days, even if you regularly log LH tests. As mentioned above, a positive LH test in itself does not guarantee that you are ovulating which is why you need to continue adding temperature data regularly if you wish to make the most of the app and understand when you are fertile.
How does logging a negative LH test influence ovulation detection?
Negative LH tests don’t influence ovulation detection. If you log a negative LH test on a given day this will not prevent the algorithm from detecting ovulation that day (or any day this cycle).
It is however recommended that you keep on logging any negative LH test that you get so you can keep track of this and better understand your cycle patterns.
A negative LH test doesn’t mean that you're not fertile, nor that ovulation will not occur – this is important to remember. It only means that no LH surge was detected at the time of the test.
Remember to continue logging your temperature every day, and the algorithm will place your ovulation should your temperatures indicate ovulation occured.