Can Twins Cause a False Negative Pregnancy Test?

You have reason to suspect you might be pregnant, but the result from a home pregnancy test is negative. Was your hunch wrong? Maybe, but there are reasons a test can produce a false negative result, meaning it says you are not pregnant, but you are.

For example, if you take a test too soon after the egg implants in the uterus, it may give the wrong result. Or you might get a false negative if you use a test after drinking lots of fluids, which dilutes your urine and affects the outcome. Using an expired test or not following the directions can also cause a false negative. And certain medical conditions or medications can make testing less reliable.

But one cause of false negatives is surprising: being pregnant with multiples. It’s rare for that to happen, but let's look at why it can.

Understanding At-Home Pregnancy Tests

At-home pregnancy tests have a 99% accuracy rate when used correctly. They detect a hormone called human chorionic gonadotropin (HCG or sometimes hCG) that the body produces when a fertilized egg implants in the uterus. If HCG is present, you are pregnant. If it is not, you are not.

Both false negatives and false positives can occur. However, if you follow the test instructions carefully and take it at the right time, it is likely to give a correct result.

That said, twins or other multiples can add a wrinkle to testing.

How Twins Cause False Negative Pregnancy Tests

You might think that being pregnant with multiples would make a pregnancy test read even more positive somehow! But in some instances, it can have the opposite effect.

A pregnancy test looks for an elevated HCG level of at least 20 milli-international units per milliliter (mUI/mL). That’s the standard amount in the urine around week 4 or 5 of a single pregnancy. When the test detects HCG at or above that level, it gives a positive (pregnant) result.

The problem arises if carrying multiples causes the level to exceed what is expected by a significant amount. In that case, the test is essentially overwhelmed by the amount of HCG and gives a negative result. There is a name for this scenario. It is called the “hook effect.” The hook effect is very rare and requires very high HCG numbers to occur.

The hook effect can also occur in the following two situations:

• Molar pregnancy - This is an abnormal type of pregnancy where something goes wrong during fertilization, and instead of a baby, unusual tissue grows in the uterus. In molar pregnancies, the hormone levels are often very high—much higher than in a normal pregnancy. This can overwhelm the test and cause the hook effect.
• Miscalculation of dates in a singleton pregnancy - A singleton pregnancy is a normal pregnancy with just one baby. If the timing of the pregnancy is misjudged—for example, if someone thinks the baby is only 6 weeks along when it’s actually 10 weeks—the hormone levels might be higher than expected for the stage they think the baby is at. If the hormone levels are unexpectedly high, it could potentially cause the hook effect.

What To Do If You’re Surprised by a Negative Pregnancy Test

If you think you are pregnant but a test says you are not, it is a good idea to proceed as if you are. Follow the advice for pregnant people concerning diet, etc., just in case.

Then, after a few days or longer, take another pregnancy test. If you get another negative result but the feeling that you are pregnant persists, contact your doctor. They may recommend a blood test, which can indicate your exact HCG level. If it is highly elevated, the focus will turn to determining if you are pregnant with multiples, likely through ultrasound imaging.

Talk With Your Baptist Health Doctor About a Potential Pregnancy

If you think you might be pregnant but at-home testing is giving negative results, talk with your doctor. They can confirm or correct what you are seeing in the tests. If you do not have a Baptist Health physician, you can find one in our online provider directory.

Next Steps and Helpful Resources

Learn More About Mother and Baby Care
How Soon Will a Pregnancy Test Read Positive?
Fact or Fiction? Pregnancy Myths Answered
Plan Your Pregnancy With Baptist Health