Top things to know about ovulation prediction tests:
Ovulation prediction kits are at-home urine tests that tell you when you’re about to ovulate
Using ovulation tests can help you time sex for pregnancy
You should start testing a few days before you expect to ovulate
Have you ever heard of ovulation prediction tests? If you’re trying to conceive, they could be a valuable tool for you. While having sex every two to three days throughout the cycle can help you conceive, this may not be feasible or desirable for everyone (1). Ovulation tests can help you pinpoint the best time to have sex or do home insemination, which can increase your odds of becoming pregnant (2).
What are ovulation tests?
Ovulation prediction tests/kits (OPKs) are urine tests that you use at home to detect when ovulation is about to occur (2). They work by detecting a sharp rise in luteinizing hormone (LH) in urine, which typically occurs 24 to 36 hours before ovulation (2). LH is produced by the pituitary gland in the brain, and a surge in this hormone signals the ovary to release an egg during ovulation (2). Timing sex after the LH surge has the highest chance of pregnancy in your cycle (3).
Some ovulation tests also identify rising estrone-3-glucuronide (E3G) levels (2). E3G is a substance that is made when the body breaks down the hormone estrogen (2). It rises before LH, around the start of the fertile window (4). E3G makes cervical mucus more wet, stretchy, and slippery, which can help sperm enter the uterus and travel to the egg (2,4). Tests that include E3G may help you identify a few extra days where there is a chance of conceiving (4).
Ovulation tests alone should not be used to prevent pregnancy (2). Ovulation tests only identify the LH surge up to 24 to 36 hours before ovulation, but sperm can survive in the body for up to five days (2,3). That means that having unprotected sex before the LH surge can result in pregnancy (5).
Choosing an ovulation test
Ovulation tests can be found at your local pharmacy or online, and vary in technology and price.
Paper test strips are the cheapest type of ovulation test. You can purchase them online in bulk, but they often don’t come with instructions. Unlike pregnancy tests, ovulation tests require you to compare the darkness of the test line to the control line, which can make it difficult to interpret the result (6). Some people prefer paper tests because they are a low-tech option that allows you to test as much as you want at a lower cost.
Digital tests that display the test result on a digital screen are the most expensive. Some digital tests are able to detect both LH and E3G, which allows them to detect more fertile days compared to paper ovulation test strips (6). To know if a test detects E3G along with LH, read the product information. While they’re more expensive, digital tests are easier to use because they interpret the results for you (6).
How to use ovulation tests
First, you need to determine when to start testing during your cycle. Ovulation tends to occur about halfway through your menstrual cycle. The best time to start testing is a few days before you expect to ovulate. So, if your cycle is 28 days long, you should start testing around day 10 or 11 (5). Most kits come with multiple tests to allow you to test over several days (2).
If your cycles are variable, use the length of your shortest cycle in the past 6 months as a guide and begin testing two to three days before the midpoint of this shortest cycle. It may take a few days of testing to detect a rise in LH.
To use an ovulation test, the tip of the strip will need to become wet with urine. You can do this by placing a few drops on it with a dropper, placing the tip in the stream while you pee, or dipping the tip into a cup of collected urine (2). Depending on the type of test you’re using, look for colored lines or read the monitor after a few minutes (2).
Interpreting ovulation test results
Results are usually displayed as a line or symbol—check your test instructions. If the test line is lighter than the control line, the test is negative, and you should continue testing for the next few days. Once you notice that the test line is becoming darker each day (i.e. that the LH is on the upswing), you can start having sex every one to two days (1). If the test line is as dark or darker than the control line, the test is positive, and it’s time to start having sex over the next two days.
Digital tests that detect both E3G and LH will sometimes identify ‘High’ and ‘Peak’ fertility days (7). A ‘High’ fertility day test result typically means that you are entering the fertile window, and you can start having sex every one to two days to maximize the chances of pregnancy (1,7). A ‘Peak’ fertility day result coincides with your LH surge, which means that ovulation will typically occur in the next 24-36 hours (7). Having sex during this time has a high chance of pregnancy.
Tracking tip: Track ‘Peak’ fertility result as a positive ovulation test in the Clue app to update your predicted ovulation date.
If you’re unable to detect an LH surge, you may have started testing too late in your cycle, or ovulation may not have occurred that cycle (8). Extending the number of testing days may improve your chances of detecting the LH surge (8). It’s also possible that your LH surge was short and the peak occurred between two tests. Testing twice a day, several hours apart, can maximize your chances of catching the surge. If you're unable to detect an LH surge for two or more cycles in a row, consider consulting a healthcare provider who can check for reproductive conditions like polycystic ovary syndrome (PCOS) that can interfere with ovulation (9).
Here are some other tips to help you use ovulation tests effectively:
Read the package instructions carefully because tests can vary. Be sure to check the expiration date (8).
Aim to test at the same time(s) every day. Some tests will instruct you to test with the first urine of the morning, and others with the second. It doesn’t really matter what time of the day you test, but it’s best to pick a time of day that works for you and be consistent (10).
Don’t drink too much water before testing. This can dilute your urine and affect the results. Avoid urination for at least four hours before testing for the most accurate results (10). This is easiest to do if you test right when you wake up.
Combine with other tracking methods. We recommend pairing an ovulation test with another method of ovulation tracking, like tracking your cycle days using Clue, or tracking your cervical mucus. You can read more about cervical mucus and other biomarkers in the Clue app Content Tab.
How accurate are ovulation tests?
Ovulation tests can identify ovulation nine out of ten times when used as directed (2). One study found that using testing methods to time sex around ovulation increases the chances of conceiving within two menstrual cycles (11).
Ovulation tests work best for people with relatively predictable menstrual cycles. They may be less reliable if:
You have unpredictable cycles. Unpredictable cycles can make it difficult to figure out when you’re due to ovulate. This means it’s more common to start testing too early or too late and miss the ovulation window altogether (2).
You have polycystic ovary syndrome (PCOS). People with PCOS may have higher levels of LH throughout their menstrual cycle, and ovulation may not occur every cycle (12). This means a positive test result may be unreliable (7).
You’re taking certain medications. Medications used in fertility treatment, other medications that contain hormones like birth control, and antibiotics containing tetracyclines can make the test result inaccurate (7).
You may also get misleading results if you’re pregnant, recently pregnant, or have reached menopause (7).
Ovulation tests can be a helpful tool in identifying your most fertile days and increasing your chances of becoming pregnant. However, if you’ve been trying to conceive for more than 12 months, or for more than six months and you’re over the age of 35, you should speak to your healthcare provider or a fertility specialist. They may recommend additional testing or treatment options to help you conceive.