Is a Faint Line on a Pregnancy Test a Sign of Miscarriage?

Interpreting Your Home Test Results Accurately

woman taking pregnancy test
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Many women repeat home pregnancy tests more than once, and then they wonder if a fainter line is a sign of miscarriage. If you had a dark line before and now you have a faint line, don't panic. This is probably just an indication that you drank more water before the second test.

What a Faint Line On a Pregnancy Test Means

Home pregnancy test results are based on the detection of the pregnancy hormone hCG in your urine.

When hCG is present, the test will return a positive result for pregnancy, and when hCG is not present, the test comes back negative. A positive result is usually indicated by two lines, either side-by-side or in a plus sign.

Given that hCG levels increase exponentially during early pregnancy, doesn't that mean the pregnancy test line should get darker and darker if the pregnancy is normal?

In actuality, things are not that simple.

Although a home pregnancy test line would probably be darker when your urine has a higher concentration of hCG, taking multiple home pregnancy tests to check the color of the line is not a reliable method of monitoring the development of early pregnancy. 

That's because the concentration of hCG in your urine will fluctuate heavily throughout the day based on how much fluid you drink, how frequently you use the restroom and other factors. Less concentrated urine means a lighter colored home pregnancy test line.

Even though you will likely pass more hCG in your urine as the pregnancy progresses and your levels increase, a home pregnancy test will not necessarily reveal a darker line hour-by-hour or day-by-day. A woman in early pregnancy who takes a test with very concentrated urine could theoretically have a darker colored result than someone in later pregnancy who tests after drinking lots of water.

Why Blood Tests Are More Reliable

Blood is far more reliable for monitoring hCG levels. That's because blood maintains a fairly steady composition at all times, thus making it easier to monitor changes in chemicals such as hCG.

The level of hCG in your blood is not affected by external factors, which is why quantitative hCG blood tests over a period of days are far more reliable for monitoring hCG levels.

If you are feeling anxious about miscarriage or if you are having any symptoms, don't waste money buying multiple home pregnancy tests. (And if you can't fight the temptation to test more than once, don't waste time worrying about light-colored pregnancy test lines.) 

Instead, speak to your practitioner about finding some other form of reassurance that your pregnancy is progressing as it should, such as a blood test.

Interpreting a Negative Pregnancy Test Result

If, however, you get a negative result on a home pregnancy test after having gotten a positive result, this could be cause for concern.

If it's not a false negative result, it could be a sign of a chemical pregnancy. This is a very early pregnancy loss. See your doctor right away so she can determine if your pregnancy is progressing normally. 

Source:

Bastian, L.A., Nanda, K., Hasselblad, V., et al. (1998). Diagnostic Efficiency of Home Pregnancy Tests. Archives of Family Medicine. 

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