Pregnancy Tests

A pregnancy test may let you know if you are pregnant.

Here are answers to some of the most common questions about pregnancy tests.

What is a pregnancy test, and how does it work?

Pregnancy tests are designed to tell if your urine or blood contains a hormone called human chorionic gonadotropin (hCG). This hormone is made right after a fertilized egg attaches to the wall of a woman's uterus.

This usually happens -- but not always -- about 6 days after fertilization. If you're pregnant, levels of hCG continue to rise rapidly, doubling every 2 to 3 days.

What types of pregnancy tests are available?

Two main types of pregnancy tests can let you know if you're pregnant: urine tests and blood tests.

Urine tests can be done at home or in a doctor's office. Many women first choose a home pregnancy test to take about a week after a missed period. Home pregnancy tests are private and convenient.

These products come with instructions. Follow them closely for the most accurate results. After testing, you can confirm results by seeing your doctor, who can perform even more sensitive pregnancy tests.

Blood tests are done at your doctor's office, but are used less often than urine tests. These tests can detect pregnancy earlier than a home pregnancy test, or about 6 to 8 days after ovulation. But with these tests, it takes longer to get the results than with a home pregnancy test.

HCG Tests

Two types of blood pregnancy tests are available:

A qualitative hCG test simply checks to see if hCG is present. It 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 a missed period. Some of these tests can detect hCG much earlier.

A quantitative hCG test (beta hCG) measures the exact amount of hCG in your blood. It can find even very low levels of hCG. Because these pregnancy tests can measure the concentration of hCG, they may be helpful in tracking any problems during pregnancy. They may also (in combination with other tests) be used to rule out a tubal (ectopic) pregnancy or to monitor a woman after a miscarriage when hCG levels fall rapidly.

How accurate are pregnancy tests?

Waiting at least a week after a missed period may give you the most accurate result. Results may also be more accurate if you do the test first thing in the morning, when your urine is more concentrated.

Urine home pregnancy tests are about 99% accurate. Blood tests are even more accurate than this.

How accurate a home pregnancy test is depends upon:

• How closely you follow instructions.
• When you ovulate in your cycle and how soon implantation occurs.
• How soon after pregnancy you take the test.
• The sensitivity of the pregnancy test.

Is it expensive or hard to do a home pregnancy test (HPT)?

You can buy a home pregnancy test in a drugstore without a prescription. The cost depends on the brand. But most tests are relatively inexpensive -- from $8 to $20.

Home pregnancy tests are quick and easy to use. They are also very accurate if you carefully follow directions. These pregnancy tests all work in a similar way. You test the urine in one of these ways:

• Holdthe test's stick in your urine stream.
• Collect urine in a cup and then dip the test's stickinto it.
• Collect urine in a cup and use a dropper to put urine into another container.

With all of these techniques, you need to wait a few minutes before seeing the results. Results may show up as a line, a color, or a symbol such as a "+" or "-" sign. Digital tests produce the words "pregnant" or "not pregnant."

If you have any questions about the pregnancy test or the results, call your doctor or the telephone number listed with the home pregnancy test.

What do the pregnancy test results mean?

It's 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, color, or sign is. If you get a positive result,you may want to call your doctor to talk about what comes next.

In very rare cases, you can have a false-positive result. This means you're not pregnant but the test says you are. You could have a false-positive result if blood or protein is present in your urine. And certain drugs, such as tranquilizers, anti-convulsants, or hypnotics, may also cause false-positive results.

If you get a negative result, you are likely not pregnant. However, you may still be pregnant if:

• The test is past its expiration date.
• You took the test the wrong way.
• You tested too soon.
• Your urine is too diluted because you drank large amounts of fluids right before the test.
• You are taking certain medications, such as diuretics or antihistamines.

If you get a negative pregnancy test result, try retesting within about a week to double-check.Some home pregnancy tests suggest doing this regardless of your results.

What if you get two different results? Call your doctor. A blood test is a good idea to confirm results.