What is a pregnancy test and how does it work?
Pregnancy tests check your urine or blood for a hormone called human chorionic gonadotropin (hCG). Your body makes this hormone after a fertilized egg attaches to the wall of your uterus. This usually happens about 6 days after fertilization. hCG levels rise rapidly, doubling every 2-3 days.
What types of pregnancy tests are available?
Two main types of pregnancy tests are blood tests and urine tests.
- Blood test
You get them at your doctor’s office, but they’re not used as often as urine tests. These tests can detect pregnancy earlier than a home pregnancy test, 6-8 days after ovulation. It takes longer to get the results than with a home pregnancy test.
The two types of blood pregnancy tests are:
A qualitative hCG test simply checks for hCG. Gives a “yes” or “no” answer to the question “Are you pregnant?” Doctors often order these tests to confirm pregnancy as early as 10 days after conception. Some can detect hCG much earlier.
A quantitative hCG (beta hCG) test measures the exact amount of hCG in your blood. You can find even very low levels of hCG. These tests can help track problems during pregnancy. Your doctor may use them along with other tests to rule out an ectopic pregnancy, when the fertilized egg implants outside the uterus, or after a miscarriage when hCG levels drop rapidly.
- Urine tests
You can take them at home or at a doctor’s office. In addition to being private and convenient, home pregnancy tests are quick and easy to use. They are also very accurate if you follow the instructions. All of these pregnancy tests work in a similar way. You taste your urine in one of these ways:
- Hold the test stick in your urine stream
- Collect the urine in a cup and dip the test stick into it.
- Collect the urine in a cup and use a dropper to put it in another container
- You will need to wait a few minutes before seeing the results.
After taking this test, you can confirm your results by seeing your doctor, who can run even more sensitive pregnancy tests.
How accurate are pregnancy tests?
Home urine pregnancy tests are about 99% accurate. Blood tests are even more accurate. The accuracy of a home test depends on:
- How closely do you follow instructions?
- When do you ovulate and how soon does the egg implant?
- How long after pregnancy is the test done?
- The sensitivity of the pregnancy test
When to take a pregnancy test?
Some pregnancy tests can detect hCG before you miss a period. But the results will be more accurate if you wait until the first day of a missed period. Results may also be more accurate if you test first thing in the morning when urine is most concentrated.
Where can I take a home pregnancy test?
You can buy a home pregnancy test at a pharmacy without a prescription. The cost depends on the brand. But most tests are not very expensive.
What do the results of the pregnancy test mean?
The results can appear as a line, a colour, or a symbol such as a “+” or “-” sign. The digital tests show the words “pregnant” or “not pregnant.” It is important to know what a positive or negative result means.
If you get a positive result, you are pregnant. This is true no matter how faint the line, colour, or sign is. If you get a positive result, you may want to call your doctor to discuss what to do next. In very rare cases, you may have a false-positive result. This means you are not pregnant, but the test says you are. You could have a false-positive result if you have blood or protein in your urine. Certain medications, such as tranquillizers, anticonvulsants, hypnotics, and fertility drugs, can cause false-positive results.
If you get a negative result, you are probably not pregnant. But you can be pregnant if:
- The test has passed its expiration date.
- You took the test the wrong way.
- You tasted too soon.
- Your urine is too dilute because you drank a lot of fluids just before the test.
- You are taking certain medications, such as diuretics or antihistamines.
If you get a negative result, try retesting in about a week to double-check. Some home pregnancy tests suggest doing this no matter what the early results are. If you take the test twice and get different results, call your doctor. A blood test is a good idea to confirm the results. If you have any other questions about the pregnancy test or the results, call your doctor or the phone number on the test.