Keke Palmer's Pregnancy-Test Snafu Is More Common Than You'd Think

In a recent episode of Keke Palmer's podcast, "Baby, This Is Keke Palmer," the actor opened up about how she and her boyfriend, Darius Jackson, found out she was pregnant (with a Pisces, no less) — and the story is equal parts funny, sweet, and relatable.

The actor took a pregnancy test on a hunch that she might be pregnant, but it came back negative. "I didn't have the lines on there, so I just threw it in the trash, you know what I mean?" Palmer said. She then went out to dinner with her friend and was drinking sake and enjoying herself — until hours later, when "all of a sudden I get a text from Darius and he says, 'When did you take this?' And it's a picture of the pregnancy test and it's positive," Palmer said. "I didn't wait long enough!"

As it turns out, Palmer's experience isn't all that unusual. Many people have a very faint pregnancy-test line when they're newly pregnant, which can be easy to miss at first. It's also possible, though, for a so-called evaporation line to form on a pregnancy test if it's been sitting out for too long, which can lead to a false-positive reading. Ahead, everything to know about pregnancy-test taking — including how pregnancy tests work, how to read a pregnancy test, and what can cause people to miss a positive result.

"Pregnancy tests work by detecting human chorionic gonadotropin (hCG), a hormone your body makes when you're pregnant," according to Cleveland Clinic. HCG can be found in both pee or blood and increases throughout the duration of one's pregnancy.

At-home pregnancy tests are typically urine based and involve peeing on a piece of reactive paper within a device (aka "a stick") that can detect hCG. HCG can be detected in urine about 10 days after conception, but experts advise that you wait until your missed period to take a test (more on that below!).

If your test is positive, you may see a plus sign, double vertical lines, or even the word "pregnant" appear. But each brand is different, so read the instructions to ensure you understand what you're looking for.

The most important thing to remember is to follow your test's instructions, since they can vary test to test and you want to make sure you're getting the most accurate result.

There are several types of tests: single-window tests (these have a control line and a second test line that indicates pregnancy); double-window tests (these have a control window and a result window, in which a horizontal line indicates a negative result and a plus sign indicates pregnancy); or digital tests (these clearly read "pregnant" or "not pregnant"). Know which type of test you have and what a positive result looks like before starting.

After taking your urine sample (you typically want to take the test first thing in the morning, when hCG levels are most concentrated in the urine), follow the instructions for how long to wait before reading the result. (You also want to make sure you're not waiting too long — more on that below.) For single- and double-window tests, even a very faint test line or plus sign means you're pregnant. But a negative result doesn't always mean you're not.

Yes. HCG levels rise quickly once you're pregnant, and today's pregnancy tests are very sensitive, so they can pick up on a very early pregnancy — but early on, the line may be more faint than later, when your hCG levels rise more, and it might take slightly longer for a test to register a positive line. So make sure to take the test as instructed. Even if your test appears to be negative at first, most say to wait a few minutes before reading the results — after two or three minutes, a positive line may appear.

In Palmer's case, she may have been a little too quick to interpret the results as negative, and a line appeared soon after she tossed it in the trash. Or the line may have been faint enough for her to miss it — but her boyfriend spotted it.

But most tests will also recommend reading the test within a certain window as well, like 10 minutes, notes Cleveland Clinic. "If a test is initially negative and you wait more than 10 to 15 minutes, you can have a faint line turn positive," explains Shieva Ghofrany, MD, board-certified ob-gyn and POPSUGAR's Condition Center advisory board member. But you run the risk of that line being a false positive, since you're outside of the window of validity for the test.

Palmer's test may have been a few hours' old by the time her boyfriend spotted it, which meant they risked seeing a false positive — but luckily, they double-checked this time. "Soon as I come home, I, and I'm also not kidding, as soon as I come home, me and him, I do 10 of 'em back to back — back to back to back to back to back. All positive," Palmer said on her podcast.

An evaporation line on a pregnancy test occurs when the urine on your test dries; it can leave a line in the results window of your test that can resemble a faint positive line. This is one reason you shouldn't wait longer than 10 minutes to read your test; during that time, urine can dry and leave an evaporation line, and the visual difference between an evaporation line and a faint positive isn't always obvious. (A faint line indicates a positive test — no matter how faint.)

One way to tell the difference between evaporation lines and faint lines: an evaporation line would be colorless, Dr. Ghofrany says, "whereas a line that is the same color [as the control line], even if it's much lighter, is considered a faint positive."

You can also get a false-negative result if you take a pregnancy test too early, "before there's enough hCG for the threshold of the test," Dr. Ghofrany says. "I tell my patients to wait until they've missed the period." While there are some tests that will detect hCG as early as five days before a missed period, she suggests waiting to avoid a misreading, which can be discouraging or even devastating.

If you can't wait and wind up taking a test before your missed period and it's negative but your period ends up being late, Dr. Ghofrany suggests repeating the test again after the missed period to be sure. (FYI, a missed period typically happens around 14 days after conception, per Cleveland Clinic.) Sometimes even a day can make a difference. But you always want to use a fresh test to avoid mistaking an evaporation line for a faint positive.