content of your saliva increases too and when the salt dries it crystallises into a fern-like pattern. A saliva-based OPK is basically a pocket-sized portable microscope, which you use to see if "salivary ferning" has occurred as your saliva has dried. The idea is that ferning is more likely to occur in the few days leading up to ovulation, helping you to identify your fertile window. How do I use them? Depending on the type of urine-based OPK, you'll either collect your urine in a cup or hold a stick in your urine stream. Coloured bands will appear on the test card or stick to indicate whether or not the LH surge is occurring. Instructions may vary slightly depending on what kit you use, but in general you should try to collect your urine between 10am and 8pm; the best time is supposed to fall between 2pm and 2:30pm. Try to collect your urine at about the same time every day, although this is not absolutely necessary. Don't test your urine as soon as you wake up, because you may miss the first day of your LH surge. Try to reduce the amount of liquids you drink for about two hours before you do the test. Too much liquid will dilute your urine, which could make it more difficult to detect the surge. The test should be read within 10 minutes for best results. A positive result will not disappear, but some negative results may later display a faint second