Can ovulation cause false positive pregnancy test

You may have heard that ovulation tests can be used to test for pregnancy. In this guide, we’ll walk through the somewhat complicated answer. 

By Dr. Kenosha Gleaton

This isn’t a straightforward answer, so let’s talk through some of the considerations and variables.

Can ovulation tests detect the pregnancy hormone, HCG?

The short answer is that ovulation tests can (sort of) act as a pregnancy test because LH is molecularly very similar to hCG. If you are pregnant, your hCG levels will be much higher than normal and an ovulation test may inaccurately detect this and read it as a high LH value. This is not to say that ovulation tests can substitute for a pregnancy test—pregnancy tests are much more accurate.

How ovulation tests work

An ovulation test is a test that lets you predict when you are going to ovulate. This is important because eggs only live for a short time after they are released—24 hours max. If you’re trying to get pregnant, you want to have sex before you ovulate to optimize your chances of getting pregnant. Sperm are relatively hearty and can survive for five to six days inside the female reproductive tract, so if you have sex before ovulation, they’ll stick around waiting for their moment to act.

There are many different types of ovulation tests, but they work by the same basic mechanism: by detecting Luteinizing Hormone (LH) in your urine. Your brain makes LH to tell your ovaries it’s time to release an egg. LH levels surge about 12-24 hours before ovulation—conveniently when you're most likely to get pregnant. 

How do the hormones LH and hCG differ?

Both hCG and LH bind and function through a common hCG/LH receptor. The biggest difference between the two is that hCG has a circulating half-life that is approximately 80-fold longer than that of LH. One study refers to hCG as a “super LH produced in pregnancy,” with 80 times the biological activity of LH.

Because the protein components of hCG and LH look very similar, an ovulation test is unable to distinguish between LH and hCG in your urine. Therefore, the right amount of either hormone in your urine will result in a positive OPK result.

What does an ovulation test look like if you're pregnant?

An ovulation test isn’t as sensitive as a pregnancy test, so it won’t pick up hCG as early as a pregnancy test will, and it requires higher levels of hCG  to turn positive. In addition, there is no way to distinguish whether the test is detecting your LH or HCG levels.

Can I use ovulation tests to test for pregnancy? 

We do not recommend using ovulation tests to determine if you’re pregnant, for several reasons:

• Ovulation tests are not as sensitive as pregnancy tests (25 mIU/mL vs 10 mIU/mL).
• It’s nearly impossible to determine if a positive ovulation test is from LH or hCG.

Therefore, you run the risk of a false negative if it’s too early and a false positive if it’s picking up LH. If you think you might be pregnant, the best and most accurate way to confirm is to use an early detection pregnancy test.

Shop Products From This Article

No matter what, taking a pregnancy test can be an emotional roller coaster. When it comes to getting a false positive pregnancy test result, the experience can be deeply upsetting, particularly for anyone who has had a difficult time getting pregnant or is actively hoping to get pregnant (or both). The hope that comes with seeing that positive sign crashing down as you realize it was a false positive pregnancy test? It's a uniquely devastating emotion. 

Of course, getting a false positive pregnancy test when you’re actively trying not to get pregnant can be just as horrible. Yup, you could probably do without the panicked verification trip to the ob-gyn, just to learn there was nothing to stress over. 

Thankfully, experts note that false positive pregnancy tests are rare. Unfortunately, though, they can happen. Here are some of the most common causes of a false positive pregnancy test, along with some additional information that can help you put it all into context.

First, what is a pregnancy test?

Let's start with the absolute basics just to make sure we're all on the same page. A pregnancy test tells you if you’re pregnant or not. That's simple enough to understand. But it's understandable if you're a little fuzzy on the details of what these devices actually look for to identify a pregnancy.

At-home pregnancy tests check for the hormone hCG. HCG is short for human chorionic gonadotropin, which the body creates during pregnancy. Right after a fertilized egg attaches to the uterine lining, the placenta then forms and starts producing hCG1. A blood test can detect hCG about nine days after conception, and a urine test can detect it 12 to 14 days after conception, according to the Cleveland Clinic, although it varies—some especially sensitive urine tests can detect a pregnancy even earlier. A person’s hCG level typically doubles every 72 hours through 8 to 11 weeks of pregnancy. Then it remains consistent and starts to go down after delivery.

Back to top.

How does a pregnancy test work?

An at-home pregnancy test is designed to find hCG in pee2. If the hormone is present, it triggers a chemical reaction and the test signals that you're pregnant. If hCG is not present, the test will say you aren't pregnant. Many tests use two lines to mean you’re pregnant and one line to mean you’re not—but it depends on the test brand. Some tests use plus and minus signs. Some digital pregnancy tests have a screen that plainly reads "pregnant" or "not pregnant." Which can save you some “Is that one line or two?!” squinting, at least.

Seems simple, right? As Ina Garten would say, "How easy is that?" Typically, pretty easy. Most at-home pregnancy tests claim to be about 99% accurate3. Ultrasounds typically can't detect a pregnancy until a little later in your pregnancy and that's why at-home tests are so useful. But, sometimes, other elements can mess with a pregnancy test's results and tell you you’re pregnant when you’re really not. 

Back to top.

What can cause a false positive pregnancy test?

Here are the most likely reasons you may end up with a false positive pregnancy test:

1. You let the test sit too long before looking.

If you take a standard pregnancy test with line indicators, it's important to check the results according to the specific instruction of the test. If you let it sit too long before reading the results, urine on the test can evaporate and make it look like you have two lines instead of just one. "Oftentimes people will see evaporation lines as urine starts to evaporate off the test," Jamil Abdur-Rahman, M.D., board-certified ob-gyn, tells SELF. That might cause the test to look like it has a faint second line—making it positive—but it really only has one.

The best way to avoid this: Read the pregnancy test's directions and follow them exactly. The popular pregnancy test brand First Response, for example, instructs users to wait three minutes after taking the test, then read it as soon as possible4.

2. The pregnancy test is expired.

The second most common reason Dr. Abdur-Rahman's patients get false positives is because the test is expired, he says. When a test is past its expiration date, the chemical that detects hCG doesn't always work as it should, and you’re more likely to get a misread. "The test can expire and the chance of having a false positive increases," Dr. Abdur-Rahman says.

3. You’re on fertility medications that raise hCG levels.

If you take a pregnancy test too soon after taking a fertility drug that contains hCG—like some injections that are often part of in vitro fertilization—you could get a false positive.

Can ovulation cause a positive pregnancy test?

Does ovulation affect pregnancy test?

Can anything else trigger a positive pregnancy test?

Can high LH cause false positive pregnancy test?