Can Expecting Twins Lead to a False Negative Pregnancy Test?

First, we need to understand how home pregnancy tests work. There are many different types of pregnancy test kits available in stores today, but they all work by detecting levels of human chorionic gonadotropin (hCG) in the urine.

Your body begins to produce this hormone once the fertilized egg implants in the uterine wall, about 6-10 days after fertilization. The presence of hCG will cause a positive pregnancy test, and the absence of hCG will cause a negative pregnancy test.

“Most home pregnancy tests can detect relatively low levels of hCG, with some brands working as early as a week before your period is due,” says Catherine Caponero, M.D., an obstetrician-gynecologist at the Cleveland Clinic in Beachwood, Ohio. Pregnancy tests are most accurate when taken after your period is late, when hCG is more likely to reach detectable levels.

In fact, if you’re having twins (or triplets, quadruplets, etc.), you may get a false negative pregnancy test result. This is because multiple pregnancies result in higher hCG levels, which can affect the results if they’re too high.

 “If your hCG is too high, it can cause a mismatch in the hCG to antibody ratio in your pregnancy test,” Dr. Caponero says.  “This can overload the pregnancy test and give you a false negative result.” 

This phenomenon is called the “hook effect,” and it’s very rare. Dr. Caponero says studies have shown it occurs in less than 2 percent of negative pregnancy tests. To experience the hook effect, your hCG level needs to be around 500,000 mIU/mL or higher, and most pregnancies only reach about half that number.

The hook effect is not just a twin pregnancy. A pregnancy test can also show a negative result despite the presence of hCG in the body for the following reasons:

• The pregnancy is further along than expected (i.e., hCG levels are high)
• There are medical conditions that can cause pregnancy, such as molar pregnancy. “Gestational diabetes is a rare complication that occurs when the egg and sperm don’t combine properly. Unfortunately, this doesn’t lead to a live birth and often ends in miscarriage or surgery,” Dr. Caponero says. 

It’s important to note that the hook effect is not very common; most of the factors that lead to false negative results fall into the realm of user error (or sometimes incorrect testing).

Here, Dr. Caponero shares some other reasons why home pregnancy tests can give you false negative results.

• A pregnancy test was taken immediately after conception.
• Your urine isn’t concentrated enough (urine becomes more diluted during the day, so most manufacturers recommend testing as early in the morning as possible)
• The pregnancy test has expired.
• Instructions were not followed correctly (e.g., the user read the results too quickly)

If the result of a home pregnancy test is negative, Dr. Caponero usually recommends waiting a few days before testing again. This is especially important if you take the pregnancy test before your period is late.

“If you think you might be pregnant or if your pregnancy test is negative and you miss your period, contact your healthcare provider,” advises Dr. Caponero. Blood tests can be done to confirm if you are, in fact, pregnant.

In the meantime, be on the lookout for these early pregnancy symptoms:

• Chest pain
• Excessive fatigue
• Cramps or back pain
• Nausea and/or vomiting
• Dysfunction
• Frequent urination
• headache
• Mood swings
• Appetite or loss of appetite