All Your Questions About At-Home Pregnancy Tests, Answered

For Allure , by Rosemary Donahue.

While trying to get pregnant can be hopeful and exciting, it can also be incredibly overwhelming — there’s just so much information out there. The wealth of information (and misinformation) about conception and pregnancy is enough to make anyone anxious. Detecting a pregnancy, however, doesn’t have to be fraught. Allure spoke with two doctors to figure out the deal with at-home pregnancy tests : how they work, how accurate they are, when to take them, and which to buy.

How do at-home pregnancy tests work?

You probably know the basic premise of how to take one, either because you’ve done it yourself or seen it play out in a movie or on TV. You go to a drugstore, buy a test, take it home (or, if you can’t wait, to a Starbucks bathroom), and pee on it. Then — depending on the test — you wait for a line or two or a plus or minus sign to show up.

As for exactly how a pregnancy test works, Ana G. Cepin, MD, an assistant clinical professor of obstetrics & gynecology at Columbia University Medical Center, says it’s a basic urine test that detects human chorionic gonadotropin (hCG) levels in the system. “hCG is produced by a pregnancy after implantation,” she explains. First there’s ovulation, then fertilization, then implantation and the secretion of the hormone.”

The higher the levels of hCG in the system (and thus, the urine), the more likely you are to get a plus sign on your pregnancy test — however, just because you get a negative result doesn’t necessarily mean you aren’t pregnant, it just may mean you took it too early. Dr. Cepin recommends that if you’ve been trying to get pregnant and you get a negative result, don’t get too discouraged — simply wait a week and try again.

When is the best time to take a test?

While you’re trying to get pregnant, it can be tempting to take multiple pregnancy tests at different times during the month, including before your missed period, but Dr. Cepin cautions against that — even for pregnancy tests that tout early detection. “Some patients may have a positive test earlier than the first day of missed period,” she says, “but this is not true across the board and [tests that tout early detection] might provoke anxiety and be too early.”

Boro Park OB/GYN ’s Diana Roth, MD says tests are highly accurate if you do them at the first sign of a missed period and your cycle is regular. (Keep in mind that sometimes even then, a negative result may not be a true negative since your hCG levels may just not be high enough for detection yet.) “As far as best time [of day] to take it,” she adds, “usually first thing in the morning [is best] because the urine is most concentrated so it’ll contain the highest levels of hCG.” You can still test later on in the day and get a positive result, but hCG levels could decrease as your urine becomes diluted.

Are false positives likely? How about false negatives?

Dr. Roth points out that false negatives can occur you miscalculate the dates of your ovulation or if you aren’t sure about them. “Women who don’t have regular cycles can’t really check the day of the missed period because they may ovulate later, and even women who have regular cycles may be ovulating later, so sometimes it can be hard to tell,” she says. “I generally tell patients that if you do a pregnancy test at your missed period and comes back negative, just wait two to three days and do it again.”

Basically, a “yes” can be interpreted as accurate , and a negative result may not stay that way. Dr. Cepin adds that miscarriages and ectopic pregnancies may also elevate levels of hCG (as can fertility drugs and other hCG-containing medication), and that you should always seek medical care if you have any concerns.

Which test is the best one to buy?

Both doctors say most tests are pretty much the same. Dr. Roth stresses that early detection (before the first day of a missed period) is unlikely for most women, because the levels of hCG in the urine will simply not be high enough. Production of hCG starts seven to eight days after fertilization, and hCG levels double roughly every 48 hours in early pregnancy . Most pregnancy tests can only begin to detect hCG levels at around 35 mIU, and around the first day of a missed period, many pregnant women’s levels are around 46 mIU — meaning chances of detection before that day are low.

Dr. Cepin does cite a study that found that out of six at-home pregnancy tests, First Response ’s manual and digital tests are around 99% accurate when taken the first day of a missed period. Based on this study, this is the brand she recommends

So, now you know — pregnancy tests measure hCG levels, are pretty accurate (especially on the first day of a missed period or after), and are kind of all the same, though First Response has research on its side. Now go forth and procreate — but only if you want to.

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