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Pregnancy Tests
Pregnancy tests are those that detect pregnancy
through the examination of a woman’s blood or urine.
ARE THERE DIFFERENT TYPES OF PREGNANCY
TESTS?
Yes. There are over the counter (OTC) pregnancy tests
which can be purchased at the local grocery store or
pharmacy and there are pregnancy tests that can be
performed in the doctor’s office.
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OTC tests are relatively inexpensive and easy to use. Whereas OTC pregnancy tests
analyze the woman’s urine, pregnancy tests in the doctor’s office involve examining the
woman’s urine and blood. OTC pregnancy tests are generally as effective as tests
performed in a doctor’s office but must be used correctly to avoid misleading results.
Technically, however, blood pregnancy tests are more sensitive than urine pregnancy
tests.
HOW DO PREGNANCY TESTS WORK?
Pregnancy tests involve the detection of a specific type of hormone. Hormones are
natural chemicals produced by the body and released into the blood that have a specific
effect on tissues in the body.
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The type of hormone detected by pregnancy tests is known as HCG
(human chorionic gonadotropin). HCG is produced in large amounts
by the placenta during the beginning few weeks of pregnancy. The
placenta is an organ in a woman that nourishes a baby during
pregnancy. HCG shows up earlier in the blood than the urine, which
is why blood pregnancy tests are more sensitive than urine
pregnancy tests. To use the home pregnancy test, the woman
removes the cover of the test strip and gathers her own urine
sample. She then dips the test strip into the urine sample. The test
strip is laid down flat where it soaks up the urine and reacts if HCG
is present. This reaction will take several minutes, with the exact
time dependent on the specific brand of test used.
A positive result is often reflected by some type of indicator on the test strip such as a line, a plus sign,
the word “yes,” etc. Results are either positive (you are pregnant) or negative (you are not pregnant).
HOW DOES ONE ACCURATELY USE HOME PREGNANCY TESTS?
To get the most accurate test results, follow the instructions listed on the box or in the package insert.
Home pregnancy tests are most accurate when the urine sample is obtained early in the morning. This is
because the initial urine in the morning is more concentrated (has less water) than urine later in the day.
The more concentrated the urine is, the easier it is to detect HCG. Home pregnancy tests can detect HCG
about 14 days after conception.
If unsure about the conception date, pregnancy tests will also work the first day after a missed menstrual
cycle. A menstrual cycle (also known as the period) is the shedding of the lining of the uterus that
generally occurs once every 28 days in women who are not pregnant. Incidentally, blood pregnancy tests
can detect HCG even before a woman has missed her period.
HOW ACCURATE ARE PREGNANCY TEST RESULTS?
Pregnancy tests are very accurate when the results are positive. That is, a woman can be almost certain
that she is pregnant if the test results indicate this. Error is more likely to occur in the opposite direction
(that a woman is pregnant when the test results say she is not). This is mostly due to using the tests
incorrectly. See above for the accurate use of home pregnancy tests. Even tests in the doctor’s office
may be incorrect if the woman’s blood or urine sample is taken too early in the pregnancy.
