It is perhaps one of the most anxiety-inducing tests a young woman can perform: a pregnancy test.
According to the claims on the back of the most popular test brands, the devices provide a result with 99 percent accuracy.
But do they do it?
A worrying clip posted to TikTok suggests that what you think you see as positive may actually not be, especially with a brand.
in a video which has so far garnered 2.5 million views, an American woman named Andie details her experience with false positive results with devices manufactured by the ClearBlue brand.
A false positive result means that a woman is told she is pregnant by a blue cross on the screen, when she is not. A false negative would imply that a line appears to indicate that there is no pregnancy, when in fact the user is pregnant.
In the video, Andie explains that she asked her husband to take a pregnancy test after realizing her period had been shorter than usual.
He bought her a test that uses blue dye to show a result manufactured by the well-known brand ClearBlue.
The mother of two explains that she “never” buys blue dye tests because “they are known for giving false positives.”
The ClearBlue test told her she was pregnant and showed a small blue cross, instead of a single line.
TikToker Andie shows off the negative result of her favorite brand of pregnancy test, which she says has “never gotten me dirty.”
However, the next day she bought a different brand, First Response, which uses pink dye, and was told she wasn’t actually pregnant.
“I always buy them,” he says, waving the pink test toward the camera. ‘I assure you, I have never been dirty. I will never take a blue dye test again in my life because last night I almost had a heart attack.
More than 2,000 users have commented on Andie’s post, sharing similar experiences with blue dye tests.
Another said: ‘Same thing happened to me with the first response! I got a crazy evacuation line a month after getting an IUD and called my OBGYN *sob* that the blood test was negative.’
Meanwhile, TikTok user Chloe said: ‘Light blue should be removed from shelves. I got so many false positives.’
Based on the series of comments on social media, it seems that the confusion lies in what is known as an ‘evaporation’ line: a faint, colorless streak that can appear in the same position as a colored line indicating a positive result.
Evaporation lines are simply a drying stain of urine and can appear if the test user waits longer than the suggested time to read the result.
The color of the evaporation line may have a slightly blue hue, so it is easy to confuse it with a positive “cross”.
It also means that women may mistake a positive result for an evaporation line and assume they are not pregnant when they are.
Market research companies estimate that more than 20 million pregnancy tests are sold annually in the United States, compared to about three million live births each year.
“I took a blue dye test and I was like ohhh, yeah, that’s an evaporation line,” said a woman named Kal, “…guess what wasn’t an evaporation line.”
Pregnancy tests work by reacting to the amount of a hormone called human chorionic gonadotropin, or HCG, in the urine.
HCG begins to be produced approximately six days after fertilization. The chemicals within the paper in the stick react with the hormone, producing a reaction that gives the dye a certain color.
The accuracy of your results will depend on when you take the test; Pregnancy can be detected from the first day of your missed period or 21 days after the last time you had unprotected sex.
Results may also be more accurate if you test first thing in the morning, when your urine is most concentrated.