Pregnancy tests detect a hormone called human chorionic
gonadotropin (hCG) in a sample of urine or blood. This hormone is produced
by the placenta after conception and is found only in pregnant
women. The amount of hCG produced during early pregnancy doubles every
two or three days and levels off in the second or third month. You
can be tested for pregnancy with an over-the-counter pregnancy test
or in your doctor's office.
How Soon After Conception Will a Home Pregnancy Test Work?
Some home pregnancy tests can detect pregnancy as early as six
days after conception, or one day after a missed menstrual period.
Home pregnancy tests are most accurate if you wait two weeks 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 never 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
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
You may get a positive test even if you are not pregnant (false
positive) if you:
Are taking anticonvulsants, anti-Parkinson drugs, hypnotics, or
Have blood or protein in the urine
How Are Pregnancy Tests Conducted in a Medical Office?
A more reliable pregnancy test—either a urine test or blood
test—is available at your health care provider's office or a family
planning clinic. An hCG urine test can be ordered as early as 10
days after a missed menstrual period. For the urine test, a urine
sample is taken 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, which
is often used to evaluate an
ectopic pregnancy. Results of these
pregnancy tests may be available the same day they are
Please be aware that this information is provided to supplement the care
provided by your physician. It is neither intended nor implied to be a
substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER
IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the
advice of your physician or other qualified health provider prior to
starting any new treatment or with any questions you may have regarding a