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22nd December 2023
03:18pm GMT
Usually, they're pretty accurate but in one unusual circumstance you may get a negative and still be pregnant - when you're having twins.
Yet the question remains, how does this happen?
It's because multiple pregnancies produce elevated levels of hCG, and if they're high enough, it can interfere with the results.
HCG is the hormone produced after the embryo implants in the uterine wall—about six to 10 days after conception.
This is what most at-home pregnancy tests use to determine if you're expecting.
As you can imagine when you're expecting more than one baby, the level can become very elevated.
Speaking to Parents magazine Dr. Caponero, said, "When hCG is too high, an improper ratio of the hCG and the antibodies in the pregnancy test can occur,
"This overwhelms the pregnancy test and causes a false negative test."
This phenomenon is called the "hook effect," and is incredibly rare.
Research suggests that it occurs in less than two per cent of negative pregnancy tests, according to Dr. Caponero.
If you want to get really science-y about it, levels of hCG need to be around 500,000 mIU/mL or higher to experience the hook effect, and in most pregnancies, they only reach about half that number.
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