Ovulation tests also known as Ovulation Predictor Kits (OPK)
 
An OPK is a quick, easy and accurate way to predict ovulation in advance. It allows you to pinpoint your fertile window from the very first month. 
 
How ovulation kits work
 
Urine-based OPKs test your urine for an increase (surge) in luteinising hormone (LH). This happens one to two days before ovulation. 
 
A small amount of LH is always present in your blood and urine. But in the days before ovulation, the amount increases by about two to five times. The 12 hours to 36 hours between the beginning of the LH surge and the moment when your egg is released is the most fertile part of your cycle. This is when you are most likely to conceive. 
 
 
How to use an ovulation kit
 
Depending on the brand of urine-based OPK, you'll either collect your wee in a cup or hold a stick under you as you wee. Coloured bands will appear on the test card or stick to indicate whether or not the LH surge is occurring. Digital OPKs use symbols, such as a smiley face, to tell you when you are on your most fertile days. 
 
Instructions may vary slightly depending on which kit you use, but in general you should try to collect your urine between 12pm and 6pm. The optimum time is supposed to fall between 2pm and 4.00pm. 
 
Try to collect your urine at about the same time every day, though 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.
 
How to read a test result 
The test line should be the same colour as the control line or darker to be classed as a positive. A faint line is a negative and a sign that the Lh hormone is present and rising (or declining if the test is taken after ovulation) .