Pregnancy tests detect a hormone called human chorionic
gonadotropin (hCG) in a sample of urine or blood. This hormone is produced
by the placenta and is found in pregnant
women. The amount of hCG produced during early pregnancy doubles every
two or three days and peaks at 7-10 weeks. You
can be tested for pregnancy with an over-the-counter pregnancy test
or in your doctor's office.
Some home pregnancy tests can detect pregnancy as early as one day after a missed menstrual period, although some pregnancies will not be picked up this early.
Most home pregnancy tests are very accurate about a week after
your first missed menstrual period.
How Are Pregnancy Tests Done at Home?
Follow the directions carefully as they differ with different
brands. Some require that you urinate directly on a stick, while
others ask that you urinate in a cup and place a small sample into
a testing well with a dropper. You will know the results in two
minutes to several hours. Results are displayed differently with
different tests. For example, some show a red plus or minus sign in
a window, others show pink or blue lines on a test strip, while
others change the color of a urine sample.
How Accurate Are Pregnancy Tests?
Home pregnancy tests are not 100% accurate. Many manufacturers
claim to have a 99% accuracy rate, but inaccurate results may be
more frequent due to improper use of the test, using the test after
its expiration date, exposure of the test to the sun, and other
factors. The procedures outlined in the instructions must be
followed exactly for the results to be accurate. Whatever the
result or the brand used, most manufacturers recommend repeating
the process several days later to confirm the results. After
conception, a woman produces a minimal amount of hCG. The strength
of each test varies, and although a woman may be pregnant, the test
may not pick up the amount of hCG hormone present the first
time.
You may get a negative test even if you are pregnant (false
negative) if you take the test too early after conception, before hCG levels are
significant.
You may get a positive test even if you are not pregnant (false
positive) if you are taking medicines that have hCG in them
How Are Pregnancy Tests Conducted in a Medical Office?
Either a urine test or blood
test is available at your health care provider's office or a family
planning clinic. For the urine test, a urine
sample is taken usually first thing in the morning. A blood hCG test
involves taking a sample of blood from a vein in the arm. A blood
test may be ordered to measure how much hCG is in the blood. The blood test can detect a pregnancy earlier than the urine test. Results of these
pregnancy tests may be available the same day they are
administered.
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