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.
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.
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.
For more information...
You can find out more about home pregnancy tests by contacting the FDA Office of Consumer Affairs
This information was abstracted from a factsheet developed by the Food and Drug
Administration.
All material contained in the FAQs is free of copyright restrictions, and may be
copied, reproduced, or duplicated without permission of the Office on Women's Health in
the Department of Health and Human Services; citation of the source is appreciated.
