What should I know about pregnancy tests?

"Am I pregnant?" is one of the most important questions a woman can ask, and she wants to get the correct answer quickly.

Today's at-home pregnancy tests are virtually foolproof and almost as accurate as those given at the doctor's office. But there are some important issues to consider when deciding what kind of pregnancy test is right for you.

At-home tests

According to most manufacturers, at-home pregnancy tests are about 99 percent effective when used as instructed. That's about the same accuracy rate as urine pregnancy tests performed in a doctor's office. The tests are available in most pharmacies and do not require a prescription.

One advantage of the at-home tests is that they allow you greater privacy and flexibility in learning the results. You can take them anywhere there's a bathroom, and they generally take only a few minutes.

Before taking the test, be sure to read and follow the directions. Be aware that the wait time for different brands may be different.

At-home pregnancy tests involve placing one to several drops of urine on a prepared chemical strip or placing the strip in the urine stream. The strip is designed to detect a pregnancy hormone called human chorionic gonadotropin (hCG). You will need to wait a certain amount of time before reading the results in the test window.

hCG is released into the body by the placenta when a woman is pregnant. This hormone also causes some of the early symptoms of pregnancy, such as breast tenderness and nausea.

hCG levels can usually be detected in the urine about 10 days after conception. If you take a urine pregnancy test fewer than 10 days after conception, the at-home tests might give a “false negative” response. This means it will show that you are not pregnant when you actually are.

Experts say women should wait five to 10 days after their period is officially late before taking the pregnancy test to make sure it is accurate. If the test is negative, wait a few more days. If menstruation (period) still hasn’t begun, take the test again and contact your doctor if you have more questions.

Here are some tips to follow when taking an at-home pregnancy test:

  • Use your first morning urine when possible (when hCG levels are most easily detected). If not, make sure the urine had been in your bladder for at least 4 hours.
  • Do not drink excessive amounts of fluids before the test to increase the volume of urine. This could dilute (thin out) the hCG levels.
  • Read the directions included in the test thoroughly before starting the test, and follow every step precisely.

Some fertility drugs or other medicines might interfere with the test results. Check the package labeling for information. In addition, if there is a problem with the pregnancy, such as an ectopic pregnancy (when the fertilized egg settles in the fallopian tube instead of the uterus), hCG levels might be low and non-detectable by an at-home test. See your doctor if you are unsure about the test's results.

Blood tests

Blood tests to detect pregnancy are rarely done as a routine measure because they are expensive, and the same results can be obtained from a urine test.

Pregnancy tests can also be done using a small sample of blood that is analyzed at a hospital or doctor's office. This blood test not only detects whether a woman has the pregnancy hormone in her body, but can also determine how much of the hormone is present. A blood test for pregnancy might be done in special circumstances, such as for women who are having infertility treatments or when the doctor thinks there might be a problem.

These blood tests are slightly more sensitive than the urine tests, as they can detect very small levels of hCG. That means they can provide a more accurate answer very early on in the pregnancy, within about nine to 12 days after conception.

For this test, a blood sample is sent to a lab for analysis. Results might take anywhere from a few hours to more than a day.

A doctor might also choose to use a blood test to compare hCG levels during the pregnancy. hCG levels usually double about every two days during the first few weeks of pregnancy. If the levels don't rise, it might suggest a problem with the pregnancy. Extremely high hCG levels might mean a woman is carrying twins or that the pregnancy may be abnormal.

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