Pregnancy Tests
How soon after conception is a pregnancy test
effective?
How do
pregnancy tests work?
How accurate are home pregnancy tests?
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How soon after
conception is a pregnancy test effective?
Regulated by the
Food and Drug Administration, pregnancy tests have come far since the
early to mid-1900's when toads, rats and rabbits were used in testing.
Now, over-the-counter home pregnancy kits provide privacy and fast
results, and can detect pregnancy as early as six days after conception,
or one day after a missed menstrual period. This gives an early advantage
for vital prenatal care.
How do pregnancy tests
work?
All pregnancy tests
are based on the presence of a hormone, human chorionic gonadotropin (HCG),
that the pregnant woman produces after conception. The first self tests of
the 1970's used ring, or "tube agglutination," tests consisting of
prepackaged red blood cells to detect HCG in urine. A ring at the bottom
of the tube indicated a positive result. Sensitive to movement and human
error, ring tests are now rarely used.
Today's brands, such
as e.p.t. and First Response, contain monoclonal antibodies that detect
minute traces of HCG. These antibodies are molecules coated with a
substance that bonds to the pregnancy hormone, if it's present, to produce
either a positive or negative result. (Each test manufacturer uses a
different "trade secret" chemical formula for the bonding substance.) The
user collects urine and combines it with the antibodies provided in the
package. The test is timed, and a color change indicates the result.
How accurate are
home pregnancy tests?
Although most
manufacturers claim 99 percent accuracy in laboratory tests, inaccurate
results may be more frequent in actual use, due to such factors as
improper use of the test, using a product past its expiration date,
exposure of the test to the sun, and cancers. The procedures outlined in
the instructions must be followed exactly for results to be accurate.
Whitehall
Laboratories markets the newest one-step brand, Clearblue Easy. It gives
results in three minutes and informs the user when the test hasn't been
done properly. This new testing method, called rapid assay delivery
system, combines a biochemical process with monoclonal antibodies in one
pen-like instrument.
Whatever the result
or the brand used, most manufacturers recommend repeating the process a
few 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.
from
The Office On Women's Health - US Department of Health and Human Services
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