What you need to know about pregnancy test results

It's easy to get overwhelmed when taking a pregnancy test. Your life could change forever depending on the results. It is important to confirm these results with your doctor, even if they are negative.

How pregnancy tests work

Pregnancy tests check the level of human chorionic gonadotropin (hCG) in the body. This is one of the first things that develop during pregnancy. This is a substance that accumulates when a fertilized egg implants in the uterus about 10 days after conception.

Types of pregnancy tests

At-home pregnancy test. The most common pregnancy test is the over-the-counter home test. These tests check the level of hCG in the urine. While the tests claim to be 99% accurate, if you follow the instructions, it's important to check with your doctor.

Home pregnancy tests have some advantages over going directly to your doctor when you think you might be pregnant for the first time:

At-home pregnancy test kits are inexpensive.
You get almost immediate results.
The instructions are simple.

Your doctor may also perform a urine pregnancy test to confirm previous results. They will also discuss with you the next steps to keep you and your baby healthy.

Blood test. This type of pregnancy test is done by your doctor. They will take a blood sample and send it. The laboratory will check the level of hCG in your blood.

A blood test is not often used during pregnancy because it is expensive and gives similar results to a urine test. A blood test is usually done for any pregnancy problem, such as if you are using fertility drugs.

Pregnancy test results

When you take a home pregnancy test, you may get a false result due to various circumstances.

False positive result. This is when a pregnancy test says you're pregnant when you're not. This may be caused by:

Contaminated urine collection cup
Damaged, expired or defective pregnancy testing kit
Blood in the urine
Protein in the urine (usually as a result of kidney damage)
Medications such as anticonvulsants, fertility drugs, diuretics or tranquilizers.
Have recently given birth or had a miscarriage
Ovarian tumor

False negative result. This is when the test says you're not pregnant, but you are. Possible reasons include:

Taking the test too early after a missed period. Repeat the test about a week after your missed period for more accurate results.
Not following the instructions. Follow the pregnancy test instructions as closely as possible, including how long you need the test to do its job.
Being too hydrated. Do the test early in the morning when your urine is concentrated. Diluted urine will not give an accurate reading of hCG levels.

The hook effect

Pregnancy tests are a type of immunoassay, a test that measures the concentration of certain particles, molecules in the material being tested. Scientists call this the "hook effect" when the weakness of the immunoassay is apparent.

The hook effect occurs when there is an excess of the analyte. The analyte of the pregnancy test is hCG.

During a pregnancy test, two molecules become "bread" on either side of the "filler", the hCG molecule. The number of hCG molecules clamped determines the results of a pregnancy test.

Too much hCG spoils the work of antibodies and antigens. HCG molecules suppress antibodies, preventing the occurrence of a molecular sandwich.

At the end of the pregnancy test, all excess molecules are washed off, leaving only a few clamped molecules. Since the abundance of hCG prevented the formation of most molecular sandwiches, a pregnancy test incorrectly shows a low level of hCG.

After pregnancy test

Focus on results. If your home test came back positive, or if you've taken multiple tests and got inconsistent results, it's time to see your doctor. They will do a blood test or an ultrasound to confirm your results.
Missing rules. After a missed period, wait a week before using a pregnancy test. Repeat the test in a few days. The sooner you use the test after conception, the more likely you are to get an inaccurate result.

If you haven't had a period but the result is negative, don't worry. There are several reasons for delayed periods: