An ovulation test can be an excellent tool to help couples that are trying to conceive to be able to predict when exactly the woman is going to be fertile, in hopes that they can time their attempt at conception so as to have a high degree of success. An ovulation test predicts fertility by helping a woman to know when she is going to ovulate.
An ovulation test predicts fertility in that it is able to test for an increase in Luteinizing hormone, also known as LH. Between 1 and 2 days prior to the time that you ovulate, you will have an increased amount of Luteinizing Hormone produced in your body. In part, this Luteinizing Hormone is responsible for encouraging your ovary to release an egg, which can then be fertilized. An ovulation test is able to predict fertility by recognizing this increased level of Luteinizing Hormone, thereby letting you know that you are about to ovulate.
A key part of using an ovulation test to predict fertility is to know when exactly you should use the ovulation test. You can get a good idea of around when you should, in theory, start to ovulate by considering the length of your monthly cycle. Most women will ovulate right around 14 days prior to the start of their next period. This means that, if you have a cycle that typically lasts 32 days, you will ovulate right around day 18. You would want to time your ovulation test 1-2 days prior to the time that you expect to ovulate.
When used correctly, ovulation tests are around 99% accurate at being able to detect the LH surge. While the LH surge does not guarantee that you are going to be able to conceive, using an ovulation test to predict fertility in this way can give you an extra edge when you are trying to conceive.