It’s normal to look at that pregnancy test result and wonder whether you can really, truly trust it. Maybe it’s not what you were hoping for—or maybe you’re cautiously getting ready to celebrate. Here’s when and why you can believe in the accuracy of home pregnancy tests.
If the result was positive, the test was probably right. That’s because pregnancy tests measure hCG (human chorionic gonadotropin), a hormone that’s excreted into your urine once you’ve conceived. If you weren’t pregnant, you wouldn’t have any hCG in your body at all.
That said, there are some circumstances that would lead to a false positive result. If you miscarried or had an abortion in the past eight weeks, or have received a fertility drug containing hCG, the hormone could show up in your urine without you actually being pregnant. Another possible reason for a false positive: If you’re testing early before you’ve missed a period, you may experience a chemical pregnancy—when a fertilized egg implants in your uterus and prompts the production of hCG, only to stop developing. If that’s the case, you’d still get your period, just maybe a day or two late.
If the test was negative, there’s still a chance you could be pregnant. The biggest factor that could affect your result is when you took the test, since it’s more likely to pick up the hCG in your urine the longer you wait to take it. Some tests have shown to sense a positive pregnancy result before you’ve missed your period, but different tests have different sensitivities. Experts say you’re more likely to get an accurate result if you wait at least five days after the day of your expected period before taking a test. If it’s been that long, you can trust its accuracy. If it hasn’t and you got a negative result, be sure to take another test again in a few days.
Expert Source: Your Pregnancy and Childbirth: Month to Month by The American College of Obstetricians and Gynecologists.
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