Can Drinking Too Much Water Cause Low hCG Levels?

Woman on a hiking trip drinking from water bottle

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Human chorionic gonadotropin (hCG) is a hormone that your body makes during pregnancy. When you take an at-home pregnancy test by urinating on a test strip, that test determines whether your body is producing hCG. If you are, it tells you that you're pregnant.

The test can't tell exactly how much hCG your body is making (it's not what scientists would call a "quantitative" test), but your body needs to be producing a certain minimum amount in order for the test to detect it.

How Drinking Water Affects Pregnancy Tests

Drinking water—or any fluids—can, in fact, affect the results of an at-home urine pregnancy test, especially when taken very early in the pregnancy. When your urine becomes diluted by drinking lots of fluids, the urine concentration of hCG becomes lower.

Take a home pregnancy test using first-morning urine that you collect before drinking any fluids.

If the level of hCG in the urine becomes so diluted that it's no longer detectable by an at-home urine-based pregnancy test, that test strip may indicate that you're not pregnant when you actually are. This is known as a false-negative test result. To avoid a false negative result, doctors recommend taking at-home pregnancy tests first thing in the morning, before you start chugging fluids.

When hCG Levels Are at Their Highest

Your hCG level rises for several weeks, peaking between weeks eight and 11 of pregnancy. It then decreases and levels off for the rest of your pregnancy.

Therefore, experiencing the type of "false negative" mix-up mentioned above is likely to happen only very early on in your pregnancy (like during the first week). After that beginning stage, even if your urine is diluted, your hCG level should still be high enough to be detectable by an at-home urine-based pregnancy test.

What to Do After a Negative Pregnancy Test

If you take an at-home urine-based pregnancy test very soon after trying to conceive and the result is negative, try waiting a few days—or even another week or two. Then take the test again as soon as you wake up in the morning to make sure that the reading was correct. Most at-home urine-based pregnancy test kits come with two strips for this very reason.

If you take a urine pregnancy test after you have missed a period and it is still negative, wait a few days and try again. If a second test still indicates that you are not pregnant, but you have not had a period, contact your physician.

Another option is to ask your doctor if a blood test that will determine whether you're pregnant with more accuracy is appropriate. The fact is, even if an at-home urine-based pregnancy test shows that you are pregnant, your doctor may still want to confirm those results with a blood test.

It's called a quantitative hCG blood test because it can measure exactly how much hCG is in your blood. In this case, the amount of water that you drink will not affect the results, as it will not alter the level of hCG in your blood, even very early in pregnancy.

By Krissi Danielsson
Krissi Danielsson, MD is a doctor of family medicine and an advocate for those who have experienced miscarriage.