Pregnancy tests seem simple enough. You pee on a stick, wait a few minutes and get your answer, right? At least that’s how it’s done in the movies.
Perhaps unsurprisingly, there’s actually much more to it than that. And before running to the pharmacy and grabbing the first box you see, it’s important to know the specifics about pregnancy tests.
Did you know that the timing of your cycle, time of day you test, and type of test you choose all matter? Or, that pregnancy tests can actually expire? There can also be false negatives and, in some cases, false positives.
With the wide range of emotions that can surround pregnancy testing circumstances, it’s important to be well informed. So, BRIDES spoke with Eric Flisser, M.D., reproductive endocrinologist and infertility specialist at Mount Sinai in New York City. Here’s everything you need to know about pregnancy tests.
The Two Types
When one thinks of a pregnancy test, typically the urine test first comes to mind. Often performed at home, the urine test is one of two types available, the other being a blood draw. Both, Flisser explains, are designed to detect human chorionic gonadotropin (hCG), which is a hormone specifically associated with pregnancy.
More often than not, urine tests are performed at home and then followed by a blood test when a woman sees an ob/gyn for a follow-up and pregnancy confirmation.
Timing Is Everything
Of course, when you think you might be pregnant, you want an answer immediately. Unfortunately, that isn’t always possible; an accurate answer largely depends on when you ovulated. Typically, ovulation occurs two weeks before you should take a test. Though, Flisser says, that can be tricky to determine unless a woman has also been tracking ovulation using other tests. As a general rule, he advises waiting until a period is late instead.
Much of a test’s reliability directly correlates with testing conditions, though both false negatives and false positives are possible. If you test too early, a result could read negative even if you do end up being pregnant. And in more rare circumstances a test can malfunction.
In this case, Flisser says, “If someone suspects the test is wrong, the best course of action would be to test again but use a test from a different manufacturer or at least a different lot from the same manufacturer. This way, if the test is defective in some way, she isn’t using a similarly defective kit that was made at the same time.”
False positives are much more rare, but two conditions can cause them. First, Flisser explains that hCG is also associated with rare cancers. So for this reason and more, “any time that a woman has a positive home pregnancy test, she should follow up with her ob/gyn for further testing.”
Sadly, there are also some true positives that may seem like false ones, but are in fact true positives—like in the case of a biochemical pregnancy. This occurs when a woman experiences a positive test result but begins her period shortly thereafter. “Biochemical pregnancies are not uncommon and often go unnoticed, especially when a woman is not intending to conceive and has not been testing for pregnancy,” Flisser says.
Much more reliable than urine testing, a blood draw can also give more information. Urine testing has a binary outcome—it is either positive or negative. Urine tests are not intended to measure the amount of pregnancy hormone and so are considered "qualitative” tests. Blood tests, however, can measure both the presence and the amount of hormone circulating in the body.
“Because of the different methodology used in the test, blood tests can detect lower levels of hormone that would not trigger a positive result in a urine test,” Flisser adds. “Because a specific amount of hormone is measured with the blood test, the change in the hormone concentration can be followed over time, and this can be useful to track the progress of a pregnancy.”
Urine Test Results
Since at-home urine tests are a yes-or-no situation, Flisser advises that any positive result should be considered a positive test, whether a digital screen or colored line tells you so. He elaborates, “Digital urine tests typically have an LCD-type graphical display (yes/no or happy face/frowny face, for example) and avoid some of the potential ambiguity of colored line tests.” Though, they aren’t really considered any more accurate than the colored line/urine dipsticks. “Even blood tests can have false positives, but only in very rare cases,” he says.
Like most things in life, timing matters. If you can wait it out, Flisser says the ideal time to take an at-home test is “generally with the first urine of the day, since that urine has accumulated in the bladder overnight and will have a high level of hormone.” Overhydrating can actually dilute the hormone in the urine below the concentration required to trigger a positive result in the test.
And, surprisingly, some pregnancy tests do expire. He advises that the manufacturer will list the expiration date on the package, so be sure to check the dates as only current tests should be used. Expired tests can give false negative results.
The Bottom Line
All positive pregnancy tests should be followed by a visit or call to a woman’s ob/gyn. Flisser also recommends that if a woman has missed her period yet has negative tests, she should also follow up with doctor.