thin blue line on a pregnancy test can change the whole of your life,
but have you ever stopped to wonder how the pregnancy test works?
is a pregnancy test and what makes it work?
pregnancy test determines whether a woman is pregnant. There are
certain markers that can indicate if a woman is pregnant which can be
found in urine and blood, and pregnancy tests are able to detect
these specific markers through an amazing process.
main marker a pregnancy test is looking for is something called hCG
(Human Chorionic Gonadotropin), which is produced by the trophobloast
cells of the fertilised egg. hCG is the most common marker that
pregnancy tests are able to find and use to determine a pregnancy.
whilst hCG is a reliable marker of pregnancy, it cannot be detected
until after implantation of a fertilised egg. This can sometimes
result in false negatives if the test of performed during the very
early stages of pregnancy.
getting a simple positive or negative, isn’t as easy as it should
be! A number of factors can mess with the outcome of a pregnancy
test. Improper usage of home testing pregnancy kits can results in
both false negative and false positives due to misunderstanding or
failing to follow the instructions included in the kits. How hard is
it to pee on a stick you’re wondering, right?
used by experienced technicians, home pregnancy tests are almost as
accurate as professional laboratory testing with 97.4% accuracy,
however when used by consumers, accuracy falls to 75%.
negative outcomes can occur when testing is done too early in the
stages of pregnancy. Most urine tests begin to detect hCG levels
shortly after implantation, which can occur anywhere from 8 to 10
days after ovulation. The levels of hCG found in urine rise
throughout the first 20 weeks of pregnancy, so accurate readings
increase as time goes on.
can take up to 12 further days for implantation to happen which can
mean even the most sensitive pregnancy tests may give false negatives
up to 17 days after intercourse.
negatives results may occur for several reasons, including mistakes
made when testing, use of drugs containing the hCG hormone and
non-pregnant production of the hCG molecule.
how does a pregnancy test work?
home pregnancy is a lateral flow test, also known as a “Sandwich
ELISA” (ELISA stands for Enzyme-Linked Immunoabsorbant Assay) this
means that the pregnancy test depends on a fluid or substance to work
out if you are pregnant or not.
job of a lateral flow test is to detect (and sometime quantify) the
presence of a certain marker in a liquid, so in the case of the home
pregnancy test, the marker is hCG and the liquid is urine.
home pregnancy test is called a Sandwich ELISA because there are
three separate zones containing capture antibodies that all perform
different things. Scientists decided that a good analogy for this was
the humble sandwich, brilliant right?
first section, or ‘slice of bread’ is called the reaction zone,
the second part – the ‘sandwich filling’ – is called the test
zone and the last section, the ‘last slice of bread’, is called
the control zone. Each of these zones is coated with capture
but they all differ from how they work and what antibodies are placed
in the sections.
on the reaction zone, the first slice of bread, will bind only to hCG
and will detach from the strip they were on upon exposure to urine.
The control zone contains a general antibody, plus a dye and serves
to let the user know that the tests outcome.
urine flows along the absorbent strip, and reaches the reaction zone
and it’s capture
If the urine used has hCG in it, the capture antibodies from the
reaction zone will be bound to the hCG molecules found in the urine
along with the dye molecules.
the urine with the hCG and reaction zone antibodies reaches the test
zone, there are obviously two possible outcomes. This is the main
definitive section of the pregnancy test and determines if you are
pregnant or not. If you are pregnant, the hCG and reaction zone
antibody complexes will bind to the test
and cause the dye to change colour (that infamous blue line) If you
are not pregnant, then the reaction zone antibodies will pass through
without triggering the dye.
control zone, the last slice of bread, is lined with general capture
and the test culminates here. The general capture antibodies will
recognise the hCG and binds to the reaction zone antibodies and
releases dye while doing so, creating a second blue line called the
Control Line and demonstrating valid test.
broken down, the pregnancy test is essentially a stick that you pee
on, but from a family planning perspective, it can change your life
in minutes. It is simple amazing to think of what goes on in that
handheld chemistry laboratory, while you are waiting with baited
breath to find out the results of something that will undoubtedly
change your whole life!
This is a collaborative post