Whilst our ovulation calculator can work out when you're ovulating based on your last period, an ovulation prediction kit (commonly referred to as an OPK) uses urine or saliva to help determine your most fertile window. Brands like Clearblue lead the way on the market, with easy-to-use test kits that are able to identify four or more fertile days. OPKs mainly come in the form of urine tests, but saliva test kits are also available (although sometimes less effective). Here's everything you need to know about how ovulation prediction kits work and which brands are best value for money. Read more about what ovulation actually means on our website.
Why are Ovulation Prediction Kits helpful?
Having sex consistently, a couple of times a week throughout your cycle, is the best way to increase your chances of pregnancy, but it is also extremely useful to be able schedule sex when you know it is likely to make the most difference, which is where OPKs come in! Couples with busy lives often find regular sex difficult and it can sometimes feel like a chore, especially for those who have been trying for a while with no success. Whilst you could chart your monthly cycles using the temperature method, with an app such as Natural Cycles, taking an over-the-counter test is a quick, easy, and reliable way to predict ovulation in advance. If your cycle is irregular, then OPKs are particularly useful. The test allows you to pinpoint your fertile window every month and plan to have sex accordingly. This can often make these times more special, as you know your chances are maximised, improving your relationship and reducing the stress often associated with trying for a baby.
How do they work?
Urine-based ovulation tests are the most common, they test your wee for a surge in the luteinising hormone (LH), which signals when you are about to start ovulating. This is detected one or two days before ovulation. Whilst a small amount of LH already exists in urine, the amount increases by two to five times in the few days before ovulation, which is how the test can reliably identify your most fertile window. During this window, you are most likely to conceive.
Salivary ferning kits are another type of OPK. These operate rather by monitoring the rise in your oestrogen levels both before and just after ovulation. You test your saliva with a tiny, portable microscope and if your oestrogen levels have risen, the salt content of your saliva increases. When the salt dries, it crystallises into a fern-like pattern, letting you know that you are now in your ovulation window. If you are not in your fertile window, the saliva will just dry in shapeless lumps.
How do you use OPKs?
These are rather like pregnancy tests, simply wee on a stick and coloured bands will appear on the stick to indicate whether or not the LH surge is occurring. If you are using a digital OPK, they usually use symbols, such as a smiley face to let you know when you are on your most fertile days. Generally, you should try to collect your wee between 10am and 8pm. The recommended optimum time is between 2pm and 2.30pm.
It is recommend that you try to collect your wee at about the same time every day, for added consistency, but this is not absolutely crucial. A few more tips - don’t do the test as soon as you wake up and try and reduce the amount of liquids you drink for about four hours before you do the test. Too much liquid could dilute your urine, which may make it more difficult to detect the LH increase.
Afterwards, read the results within ten minutes and throw the test away once you’ve read it, as sometimes faintly coloured bands start appearing sometime after, which can deceive you about the result.
Salivary Ferning OPKs
Using a salivary ferning OPK is easier, simply place some of your saliva on the slide, either using your finger or licking it. Do this first thing in the morning, before you’ve had anything to eat or drink. Make sure you don’t put too much saliva on it and that it is free of any air bubbles for the best result.
Then, you wait for the saliva to dry and use the microscope to see whether there is any ‘ferning’ or not. You can compare your slide with examples in the instructions to see whether you are ovulating or not that day.
With both types of OPK, the best time to start testing is on day 11 of your cycle and you can carry on for six days. Our ovulation calculator will help you with that.
Is there anything else to be aware of when using OPKs?
Although over the counter drugs like paracetamol won’t affect the tests, those containing Human Chorionic Gonadotrophin (hCG) or LH can have an effect on your result. Equally, some fertility drugs can also skew the test results, so make sure you check the back of any medication before taking the test.
Urine-based LH tests are 99% accurate at detecting ovulation. Salivary ferning tests aren’t as accurate, as the process of ferning may happen at other times in your menstrual cycle, especially if you are taking fertility drugs. One thing to note is that if you have poor eyesight, salivary ferning kits may not be the best method to choose.
How much do they cost and which brands are best?
Standard urine-based OPKs are priced between £10 and £15 per cycle. Most brands offer the same level of reliability, so definitely pick the one that offers you the most tests for the least amount of money.
On the market at the moment, we recommend the Clearblue Digital Advanced Ovulation Test for ease of use and for best value for money, the One Step Highly Sensitive Ovulation Strip Test.
Salivary ferning OPKs can be better value. After the initial cost of between £20 to £35 for the microscope, you should be able to use it again and again. However, if it takes you a long time to conceive, you might have to replace it after about two years. We recommend the Fairhaven Health Fertile-Focus Ovulation Microscope.
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