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How
do pregnancy tests work?
by Tash
Hughes
Most women know that a pregnancy test requires a urine sample, preferably first
thing in the morning. They know that a colour change or new line appearing
(depending on the test brand) will mean pregnancy, either wanted or not. But how
do these tests work?
Beta Human Chorionic Gonadotropin Hormone,
b-HCG, B-HCG or even βHCG, is released by a woman’s body upon implantation of a
fertilized embryo. This occurs approximately eight days after
fertilization.
This hormone is responsible for encouraging
the corpus luteum (or centre) of the embryo to release progesterone and
oestrogen early in the pregnancy. By about 8 or 9 weeks of pregnancy, the
placenta will take over this function and the βHCG levels will drop by 70 – 90
%. If high levels are detected between 15 – 22 weeks of gestation, it indicates
problems with the embryo and this is the basis of the Triple Test for genetic
disorders such as Downs Syndrome.
βHCG levels can be measured in
International Units per Litre (IU/L) or International milliunits per millilitre
(mIU/mL.) For men, the level is usually less than 3 whilst non-pregnant women
have a level below 5, or 10 if she is menopausal.
There is no agreement on a particular level
of βHCG representing pregnancy, as there is variation between women and
foetuses, and even differences between pregnancies of single and multiple
foetuses. Effectively, though, if a premenopausal woman tests for more than 5 it
can be assumed that implantation has occurred.
Pregnancy tests that use a urine sample are
all based on detecting higher levels of βHCG. Different tests have different
sensitivities, often varying between 15 and 25 mUI/mL, and thus can be more or
less effective very early in the pregnancy. Most tests in Australia have
sensitivity greater than 20mIU/mL.
Tests available from www.downunderptopk.biz
test for 20mIU/mL of βHCG and thus can be used as early as 6 days after
ovulation, which is before the woman even expects to have a period. A result can
be seen as soon as 40 seconds later, but clearer results require 5 minutes. This
Australian site sells the tests for only $2 each, compared to $10.39 for 2 tests
at Coles and $6.28 for one test at Safeway.
Tash
Hughes is
the owner
of
Word
Constructions
and
assists
businesses
in
preparing
all
written
documentation
and web
site
content.
Tash also
writes
articles
for
magazines,
newsletters
and
websites.
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