Like traditional pregnancy tests, digital versions work by testing your urine for the hormone human chorionic gonadotropin (hCG), which your body starts to produce shortly after conception. Digital tests look like a pen-shaped instrument instead of a traditional stick, and rely on a method called "rapid assay delivery," which can give results in only 3 minutes and even tell you if the test wasn't done properly. This method combines a biochemical process with antibodies that detect hCG. You can buy one at any drugstore; they're a simple, fast, and private way to confirm that you're expecting.
Some women prefer digital pregnancy tests for their ability to pick up on pregnancy before a missed period. The most sensitive digital tests can detect concentrations of hCG as low as 15 milli-international units per milliliter (mIU/mL) versus the 25-40mIU/mL mark non-digital kits need. For reference, the American Pregnancy Association says hCG levels less than 5mIU/mL occur naturally in non-pregnant women, and anything between 6 and 24mIU/mL is a "gray area." The farther along you are in pregnancy, the greater your levels of hCG are likely to be.
How Do Tests Detect hCG?
The pregnancy test sticks or cups which catch your pee contain antibodies coated with a chemical that bonds to hCG if it's present, delivering a positive result. If the molecules do not bond with any hCG, you get a negative result. However, because hCG levels are very low early in pregnancy and ramp up as your pregnancy progresses, it's possible to get a negative test result (but actually be pregnant) if you test too early.
If you suspect that you've done the test too early, before there is enough hCG in your urine, wait a few days and repeat the test. If it is still negative and you haven't gotten your period, something else may be happening in your body. Certain medications and illnesses can cause you to skip a period, as can excessive exercise, low body weight, early menopause, birth control pills, or stress.
How Accurate Are Digital Pregnancy Tests?
It depends on the timing. For example, the manufacturer of the First Response Gold Digital pregnancy test claims it is 99 percent accurate when taken one day before your expected period, but that accuracy rate drops to 60 percent if done 5 days earlier. Inaccurate results may be due to improper usage (in which case your digital test should indicate as much), use of a product past its expiration date, exposure of the test to sunlight, and the presence of cancer in the user. It's very important to test in the morning when hCG concentration is highest and follow the package instructions exactly for results to be accurate.
Regardless of the brand used or result obtained, most manufacturers recommend repeating the process a few days later to confirm results, because levels of hCG following conception are so low. The strength of each test varies, and the test may not pick up the amount of hCG hormone present the first time you test.
How Long Does a Digital Pregnancy Test Stay On?
According to test manufacturer Clear Blue, its test results remain on the display window for approximately 24 hours, and users of other tests report their results stayed visible from 3 to 15 hours. If you're planning to use the test to surprise your partner or family with pregnancy news you may want to take a photo of the readout or take a second, traditional pregnancy test, which lasts much longer.
Should I Get a Blood Test?
After testing positive on a home pregnancy test, some women like their doctors to confirm pregnancy with a simple blood test. These tests are way more sensitive than urine tests, so they can detect a pregnancy almost immediately after conception. (This is ideal for women who need to discontinue certain medications as soon as they learn they're pregnant, for example).
In the past, doctors almost always used to confirm home test results with an in-office blood test, but because today's home pregnancy tests are much more sensitive and accurate than older versions, many offices no longer do this. Still, it's important to make an appointment with your OB/GYN as soon as you think you're pregnant, to get the prenatal care you and your baby need as early as possible.
Selections of this article originally published in You & Your Baby: Pregnancy.