Ovulation tests: 5 reasons you might get a false positive

Trying for a baby comes with a big dose of uncertainty. While 85% of couples trying for a baby will get pregnant within a year, that can add up to a lot of two-week waits (the nail-biting window between ovulation and your period’s due date), especially if it’s taking longer than you expected. 

Anything that makes trying to conceive (TTC) a little more predictable is generally helpful, like ovulation tests, for example. Designed to flag when you’re at your most fertile time of the month, ovulation tests can reassure you that you’re having sex at the prime time for getting pregnant if that’s your goal. And if sex needs a little planning for some reason — one of you works away from home, for example — knowing when you’re ovulating can help you make it count.

Research suggests ovulation tests are up to 99% accurate. But that’s not to say they’re completely foolproof — they may sometimes give false positive results. In other words, they might wrongly suggest that you’re about to ovulate. Let’s find out why this happens — and if there’s anything you can do to help make your test reading more accurate.

Key takeaways

• Ovulation tests are designed to detect levels of a hormone called luteinizing hormone (LH) in your urine. The amount of LH in your system sharply rises around 36 hours before you ovulate, making it a telltale sign you’re about to release an egg.
• These tests are usually accurate at predicting ovulation, so they can be helpful for planning pregnancy sex.
• Occasionally, however, you may get a false positive from an ovulation test. There are a few reasons this can happen, and some can give you useful clues about your health.
• You can boost your chances of an accurate result by making sure you’re using the test correctly and understanding more about your usual cycle. 

What does a positive ovulation test mean? 

Ovulation tests work by picking up raised levels of luteinizing hormone in your urine. LH plays an important role in ovulation by telling your ovary to release an egg. You get what’s called an LH surge around 36 hours before you ovulate, and the egg then survives for 12 to 24 hours after ovulation in the hope of being fertilized by a sperm. That means that the day you get that positive result is a great time for pregnancy sex — and so is the day after. But, as Dr. Renita White, obstetrician and gynecologist, US, points out, it’s a prediction of ovulation — not a guarantee: “A test can detect the LH surge, but it can’t tell if you ovulated afterward.”

Why is my ovulation test always positive?

The idea of ovulation tests is that if you take them over a period of time (say, a week around the middle of your cycle, for example), you’ll spot when the tests turn from negative to positive. Then, you’ll know when you could have a chance of conceiving. So it might be surprising to find your daily ovulation tests show a positive result for longer than you expect. The thing is, this doesn’t necessarily mean it’s giving you a misleading result. 

One study found that the length of the LH surge can vary a lot between women, so yours may just be longer than average. It also pointed out that LH can hang around for a while after you’ve ovulated, so this could be why the test is still reading positive. Plus, you may be picking up the LH rise right at the start of the surge, which can mean you get positive results for longer.

Having said all that, more than 7% of positive ovulation test results are false. So unexpected positives can be worth questioning if you’re not sure. There may be some other clues that your results are off, too. These can include “positive tests at times that don’t make sense — such as a few days after your period ends or during your actual period,” says Dr. White. 

Positive tests at different times each month could be another warning sign. “If you have a regular menstrual cycle, you should have a predictable fertile window,” says Dr. White. “A test that turns positive at random times could suggest a false read.”

You may also be alerted to an inaccurate result if you’re using other ovulation-tracking methods — like the Flo app or looking out for physical signs of ovulation, for example — and you find that they don’t match the positive test. The most obvious clue you’ll notice physically is a change to your cervical mucus, which becomes like stretchy, raw egg white during your fertile days.

 And if you’re having fertility investigations, you may spot that you’ve had false positives if your health care provider’s tests show you haven’t ovulated when your test predicted you would.

What could cause a false positive ovulation test? 

There are a few things that could cause a false positive result on an ovulation test, including:

Polycystic ovary syndrome (PCOS)

A hormonal disorder that affects between 8% and 13% of reproductive-age women, PCOS often causes imbalances in certain hormones. And that includes LH. “Women with PCOS may have naturally higher levels of LH,” says Dr. White, “so your ovulation test can read positive even when you’re not about to ovulate.” In fact, women with PCOS can experience anovulation, when no egg is released in some cycles.

Not everyone has the same symptoms, but signs of PCOS can include irregular periods, acne, and excess face and body hair due to high levels of sex hormones called androgens. Your ovaries may be enlarged, with lots of small follicles that often can’t release eggs. That said, you can still be diagnosed with PCOS even if you don’t have cysts on your ovaries. Chat with your doctor if you think you might have PCOS.

If you have PCOS and you want to get pregnant, you may need a little help, so speak to your doctor about it. But rest assured, most women with the condition can still have a baby if they manage the condition with treatment, which can range from lifestyle tweaks to fertility drugs.

Perimenopause

Perimenopause is your transition through menopause. It covers the years leading up to menopause (which is your last ever period) and the 12 months after, at which point you can be sure you’ve reached menopause. It’s also a time when your hormones can be erratic, rising and falling unpredictably.

“Later in perimenopause, as your ovaries run out of eggs, levels of follicle-stimulating hormone (FSH) and LH get higher and higher,” says Dr. White. As your ovaries release fewer eggs, your body makes more hormones to try to trigger ovulation. “You can get an LH surge, but ovulation doesn’t happen,” she explains.

If you’re anywhere between your late 30s and your 50s, but most commonly, your 40s, perimenopausal hormones are a potential cause of those LH false starts, especially if you’ve noticed other symptoms, such as irregular periods, anxiety, or hot flashes. This idea may feel hard if you’re hoping to have a baby, but don’t lose hope. Find out where you stand with a visit to your health care provider — they can talk through your options.

It’s rare, but not impossible, to go through premature menopause, when you stop ovulating and having periods before 40. This isn’t the same as a condition called primary ovarian insufficiency (POI), which may also be a cause behind a false positive ovulation test. Having POI means your fertility is reduced, but you might still ovulate at times. If you’ve missed your period for three months or more, see your health care provider. While it can be easy for your mind to run away with you, try not to worry before speaking with them. There can be other reasons your periods are hit and miss, including stress, says Dr. White, so it’s always worth getting checked out.

Prescription fertility medication 

Fertility meds may affect your ovulation test results. For example, to stimulate your ovaries and trigger ovulation, you may be prescribed Clomid or medicines called gonadotropins, which can both raise LH.

Ovulation tests do have a role in fertility treatment, though. “Your doctor may ask you to use them at home — as well as having other tests in their office — to help confirm the medicines worked and what time you ovulated,” says Dr. White. “This may be different than your typical menstrual cycle timing [which is ovulation roughly midway through your cycle].” 

Pregnancy

There’s a chance your false positive ovulation test could be due to the fact you’re already pregnant. When you conceive, the human pregnancy hormone human chorionic gonadotropin (which you might have heard of as hCG) shows up in your urine 12 to 15 days after you ovulate. HCG is what a pregnancy test searches for. 

Admittedly, hCG’s arrival is more likely to show up around the time your period is due — not the time you’d normally reach for an ovulation test. But you may test at other times of the month — for example, because you’re trying to track irregular cycles or you’re just curious — so there’s a chance the test may pick up on hCG rather than LH. “The look and shape of the hCG molecule mimics the look and shape of LH,” explains Dr. White.

If you’ve missed a period and think you might be pregnant, then it’s worth taking a home pregnancy test. Your doctor can also do a blood test to figure out if you’re pregnant.

Thyroid conditions

The thyroid gland in your neck is responsible for releasing hormones that keep your metabolism in check (aka converting the food you eat into energy). Sometimes, though, your thyroid can be out of whack, either producing too much or too little of the hormones you need. 

“If untreated, an underactive thyroid (hypothyroidism) or an overactive thyroid (hyperthyroidism) can cause issues with ovulation and periods,” says Dr. White. This means having a thyroid imbalance could mess with your ovulation test results. “Thyroid stimulating hormone (TSH) molecules look similar to LH, so an ovulation test may falsely read as positive when it’s picking up TSH,” explains Dr. White. 

Symptoms linked to thyroid conditions include “irregular periods, weight changes, dry skin, and brittle nails, although these can be subtle,”  notes Dr. White. She adds: “It’s not likely a false positive ovulation test would be your first sign of thyroid problems. But, if you have several new symptoms along with false positive tests, your doctor can [help].” 

Treatment is available to help your thyroid work properly — and it can help boost your chances of conceiving, too.

How to avoid false positive ovulation tests

Sometimes, misleading results are due to plain old human error, so try these best practice tips to improve your chance of an accurate test.

• Start testing every day four days before your predicted ovulation day, which is around day 14 in a standard 28-day cycle. But we all know there’s no guarantee our menstrual cycles will always be 28 days. If yours is shorter or longer, your ovulation day will be different. You can use the Flo app to see when you’re likely to ovulate each month.
• Get to know physical ovulation signs and symptoms — like clear, wet, slippery cervical mucus and a change in your basal body temperature, for example — to help you test at the right time. Flo can teach you what to look for. “It can be useful to test a day or so before your fertile window so you can see an LH surge that may occur earlier than you expect,” says Dr. White.
• Testing in the afternoon can make a difference, says Dr. White. “Your body secretes LH in the morning, but it takes several hours to reach your pee, so a test may only be positive in the afternoon, ” she explains. 
• Testing twice a day could improve your chances if your LH surge is short. But it’s up to you.
• Avoid drinking too much fluid before you test — it may dilute your urine, so the test doesn’t pick up the LH.
• Make sure you know how to read your ovulation test. Some tell you you’re about to ovulate with a color-changing line next to a control line, while others use words or smiley faces.
• It may sound obvious, but test kits can differ, so always read — and follow — the directions.

A final word on ovulation tracking

Getting to know your unique cycle is always a good idea. When it comes to ovulation tests, it can help you pinpoint the right time to test, which can prevent a lot of wasted test strips, especially if your periods are irregular. Plus, being familiar with the physical signs of ovulation may help you feel more confident in the test result.  

An ovulation-tracking app like Flo can make it easy to track your cycle, get a prediction about when you’ll ovulate based on your own personal cycle history, and arm yourself with expert information and resources. Download Flo today for free.