How to Use Ovulation Test Strips to Detect Fertility

How ovulation predictor kits work and how to use them

Pros and cons of ovulation predictors

Verywell / Cindy Chung  

Ovulation test strips are urine tests that you use at home to detect impending ovulation. They work by detecting the luteinizing hormone (LH), which increases to prompt the release of the egg during ovulation. Sometimes they are called ovulation predictor kits (OPKs), or simply ovulation tests.

An ovulation test kit may come with several paper test strips, or the test may look more like a pregnancy test stick. You either pee on the extended tip of the pregnancy-test-like version, or you pee in a cup and then carefully dip the test strip into your urine.

The results can tell you if you might be ovulating soon. Using ovulation strips can help you time sex for pregnancy. Typically, when you get a positive result on the test, you should have sex every day for the next several days.

However, your OB/GYN can give you specific guidance on the optimal timing and intercourse frequency for you and your partner. Learn more about taking an ovulation predictor test and how to interpret the results.

Do Ovulation Test Kits Work?

Some studies show that ovulation testing can increase your odds of getting pregnant. However, for them to be effective, you need to do the test correctly and have sex during the indicated time period.

Other research has found mixed or limited results or no increase in pregnancy rates at all. Lab testing for ovulation has been found to be more effective. That said, studies also show that people using ovulation kits tend to feel good about the experience and think they were helpful.

Another option is to simply have sex every day or every other day between days 8 and 19 of each menstrual cycle (day one is the first day of menstruation). However, if you don't have the time or inclination to have sex that often or your period is irregular, an ovulation kit can help you pinpoint your most fertile days.

How to Choose an OPK

There are a variety of ovulation predictor kits available. Clearblue Easy and First Response are the most popular. Like pregnancy tests, you can pay relatively little or quite a lot, depending on how much technology you want. The most expensive OPKs are digital.

The Clearblue Easy Fertility Monitor is one of the more popular digital tests. This monitor detects two hormones, LH, and estrogen. This allows it to detect more fertile days than paper ovulation test strips.

Paper test strips are the cheapest type of ovulation test. You can purchase them online in bulk, but they often come with no instructions for use. Unlike a pregnancy test where you either have a line or you don't, an OPK test requires you to decide if the test line is darker than the control line. That's not always easy to determine.

What you choose to buy and use has more to do with your comfort and ease in reading the results. A digital monitor takes the guesswork out of ovulation testing. However, they are significantly more expensive.

Despite the slightly increased difficulty with result interpretation, some people love the test papers. One advantage is that this low-tech, low-cost approach frees you to quickly test as often as you'd like.

How Ovulation Tests Work

Ovulation predictor kits work by detecting the levels of luteinizing hormone (LH) in the urine. As ovulation approaches, LH spikes in order to push the egg into the final stages of maturity. This spike of LH is called the LH surge. It happens about 36 hours before ovulation.

The chance of pregnancy is highest when sperm are present in the fallopian tubes at the time of ovulation. So it's ideal to have sex during the 3 to 5 days prior to ovulation (to give the sperm time to travel from the cervix to the fallopian tubes).

Since OPKs detect the LH surge that occurs 12 to 36 hours before ovulation, you'll know when to start having sex at just the right time for conception.

The Clearblue Easy Fertility Monitor detects LH and estrogen. Because estrogen begins to rise before the LH surge, the Clearblue Easy Fertility Monitor can give you more warning that ovulation is coming. This will allow you time conception sex for up to a week before you ovulate.

How to Use an Ovulation Test Kit

Be sure to read the instructions of your particular ovulation predictor kit, if available, since there may be slight variations on how they work. Generally, however, an ovulation predictor kit comes with a set of five to 10 test strips or sticks.

Begin using the tests about two days before you expect to ovulate. If you’re not sure when you ovulate, you can use an ovulation calculator or chart. There are also fertility apps that can help you estimate when ovulation is likely to occur for you. 

The exception is the Clearblue Easy Fertility Monitor. For this product, you need to start testing on the first day of your period.

If your cycles are irregular, test according to the earliest and latest dates you’d expect to ovulate. It helps to have a kit with several test strips if this is your situation. Consult your OB/GYN if you need help determining the best timing for your body.

Ovulation predictor kits have two lines. One line is the control line. This just lets you know that the test is working. The second line is the test line. When the test line is as dark or darker than the control line, LH is surging. This is when you should start having baby-making sex.

If you test for five days, you have an 80% chance of predicting ovulation. If you test for 10 days, you have a 95% chance of predicting ovulation.

Pros and Cons of OPKs

Pros
  • Relatively easy to use. Unlike charting your body basal temperature (BBT), you don’t have to remember to have a thermometer right by your bed or avoid moving too much when you wake up.

  • Unlike BBT charting, ovulation predictor kits tell you when ovulation is approaching, not that it's already passed. Unless you're also checking your cervical mucus, a BBT chart can’t tell you when you should have sex.

  • Ovulation kits don’t need to be used right when you get up. Morning urine is best, but taking the test within the same six-hour window every day should give accurate results.

  • If you're not comfortable checking for cervical mucus, you may feel better using the test strips.

Cons
  • Using one month after month can get expensive. This is especially so if your cycles are irregular and you need to use more than five test strips.

  • Some people have trouble reading a positive ovulation test result. If you don’t get a very strong LH surge, it can be difficult to tell whether the test line is as dark as the control line.

  • Ovulation tests may not work well for people with polycystic ovarian syndrome, who can have several LH surges or high levels of LH throughout their cycles.

  • Ovulation kits sometimes yield false-positive results. So, you may think you're ovulating when you're not.

  • They can signal that your body is trying to ovulate, but they can't confirm that ovulation happened. It's possible for LH to surge but an egg to never release.

While ovulation predictor kits cannot confirm that ovulation actually took place, body basal temperature charting can. Ovulation predictor kits can be used alongside other methods of ovulation detection like BBT charting or checking cervical mucus. This can give you more assurance and help you get to know your body better.

You may want to use an ovulation predictor kit when you start fertility charting for added confidence. Once you get the hang of charting your BBT and cervical mucus, you can likely drop the ovulation test strips. For people who find fertility charting stressful, though, ovulation predictor kits can be a great way to predict ovulation and time sex for pregnancy.

Analyzing the Results

If your test reads positive, you know to start having sex daily or every other day over the next three to five days. However, sometimes, you might go through your ovulation test strips but never get a result indicating ovulation. One possible reason is you started testing too early in your cycle.

Let’s say you have an ovulation kit that contains five tests and you started testing on day 13 of your cycle. Day 17 would be your last test day. But if you don’t ovulate until day 25, for example, you may not get a positive result because you weren't testing on your most fertile days: Days 22, 23, and 24.

Another possibility is you started testing too late. For example, if you ovulated on day 12, but didn’t start testing until day 14, you would miss the LH surge.

This is one reason it helps to have an idea of when you tend to ovulate. The longer your cycles are, the more likely it is that you ovulate later than average. The shorter your cycles are, the more likely it is that you ovulate earlier than average.

Another possible reason you won’t get a positive result is you’re not ovulating. It’s not abnormal to have one off cycle once in a while. However, if you don’t get a positive result after a few months, or if your cycles are irregular, talk to a healthcare provider.

Detecting Early Pregnancy

You may have heard that ovulation tests can be used to detect pregnancy. The answer is yes, they can! However, they are nowhere near as accurate as a pregnancy test. The reason that ovulation tests can act as a pregnancy test (kind of) is that LH (the hormone that ovulation tests detect) is molecularly similar to human chorionic gonadotropin (hCG, the pregnancy hormone that pregnancy tests detect).

So theoretically, if you’re pregnant, and you use an ovulation test, you may get a positive result. However, it’s also very possible for you to be pregnant and for an ovulation test to not return a positive result. You might think you’re not pregnant when you really are. Pregnancy tests are much more reliable.

A Word From Verywell

Ovulation predictor kits can be a helpful tool in determining the best timing for sex in order to conceive. While they aren't strictly necessary, they can help increase your odds of getting pregnant. Consult with your doctor if you have questions about your ovulation timing, how to use ovulation test strips, or if ovulation prediction kits are recommended for you.

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6 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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