You take the test and watch the line appear… or not. If pregnancy has been elusive, the home pregnancy test (HPT) can be a symbol of the dream that holds all your hope and joy—or your fears and disappointment.
So what about that nebulous faint line—are you or aren’t you pregnant?
How home pregnancy tests work
HPTs generally have two lines. One line is the control line—it is usually darker and indicates that the test is working properly. The other line is the test line that indicates pregnancy by detecting the hormone human Chorionic Gonadotropin (hCG), which is not usually present in your body otherwise.
HPTs use antibodies to bind hCG and produce a reaction, which results in a color change in the test line. The strength of a positive test line depends on the amount of hGC in your urine.
A true line is considered a positive pregnancy test—even if the test line is so faint, you can barely see it.
In a typical pregnancy, your hCG level doubles every 48 to 72 hours, reaching its peak around week 10, after which levels decrease and then plateau for the remainder of your pregnancy. If the line that appears within a few minutes of taking the test is faint, it usually means that your hCG level is low. This doesn’t always mean your pregnancy is in danger. It could be just because at the time you tested, your hCG level is high enough to trigger the test.
Read more: The surprising history of home pregnancy tests
Reasons why you might see a faint line on your pregnancy test
- You’re still very early into your pregnancy. Some very sensitive pregnancy test kits can detect pregnancy as early as six days before your missed period, but the levels of hCG this early can be so low that you can expect any line to be faint.
- You’ve drunk too much liquid. Drinking a lot of liquid before testing can dilute your urine sample, which is why HPTs recommend you use your first-morning urine samples for pregnancy testing.
- You’re experiencing a chemical pregnancy. When implantation of a fertilized egg happens, hCG is produced, even though that egg may not be viable. A chemical pregnancy is one that occurs before the fifth week of gestation, far before a baby can be visibly detected on an ultrasound. If you become pregnant and then lose the baby, there may be enough residual hCG in your urine for an HPT to detect, which could produce a faint line.
- You might be testing too early in your cycle. If you test earlier than 10 to 12 days past ovulation, the hCG concentration in your urine may not be high enough to produce more than a very faint line.
- Different tests have different sensitivities. Some HPTs are good for testing before you’ve missed your period, but others might not be. If you want to test early, make sure you use a test that can detect lower levels of hGC.
- Your HPT has expired. An expired test may look and feel like a regular pregnancy test, but the results may be compromised.
But don’t worry—if you had a dark line before, and now that you have retested (because, well, we have to be sure) there is a faint line, there could be another explanation for this, other than your hCG levels are dropping because you are having a miscarriage. Another reason for a faint line could be that it is an evaporation line.
What is an evaporation line?
Evaporation lines happen when the urine that was on the test area starts to dry. The chemical composition of the urine sample changes due to evaporation and the test may start to show a positive line. The pregnancy test looks like it’s positive—there seems to be some sort of a faint line—but it’s actually not a true positive result.
An evaporation line rarely has any color to it. It’s more like a faint line where you would expect to see a pink or blue line. And an evaporation line usually doesn’t appear on a test if you look at it during the recommended time frame.
For instance, a pregnancy test may tell you to look at the test three minutes after taking it, but not after 10 minutes have passed. It’s important to follow these directions to avoid misreading your pregnancy test.
Wanting (or not wanting) to be pregnant can make you really doubt yourself when reading a HPT. Studies have shown that for various reasons, 1 in 4 women can misread line-based pregnancy tests.
One way to avoid any reading errors due to incorrect results is to take a digital test where an optical sensor displays the words “Pregnant” or “Not Pregnant” and eliminates the need for you to interpret the result yourself.
Most likely, if you see a positive line on your HPT, even if it’s faint, you are almost certainly pregnant. But if you do see a faint line and you’re still not sure whether or not you are pregnant, try waiting a day or two to take another test to give your body a chance to build up its hCG. And always use a sample from your first-morning urine, which is more likely to have higher concentrations. And then if you’re still not sure, see your doctor.
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