I’ve always thought it amazing how with just a piece of paper, pee and five minutes
of your time you can find out whether you’re pregnant or not.
However, as simple as pregnancy tests are to use, they are actually a feat of biochemical
engineering, and today I’m going to tell you exactly how they work, and how they can
not only inform us about pregnancy, but they can also help us with the diagnosis of prenatal
conditions and certain types of cancer!
[Intro by Cristina de Manuel & Caro Waro] In Ancient Egypt, women used to pee on barley
and wheat plants to find out if they were pregnant, and a few days later, if the plants
had grown, it was a sign that they were pregnant, and the plant that had grown the most would
determine the sex of the future child.
Now, whilst this may sound like a p1$$-take, the Egyptians were actually on the right track
when using urine as a means for detecting pregnancy, and even more surprisingly, a modern
study showed that the plant growth was accurate in detecting pregnancy on 70% of the occasions.
[Not so much so for detecting the sex of the future child mind you!]
Now, the reason for this is that a hormone produced early on during pregnancy is capable
of stimulating growth in plants – and very conveniently, is excreted through our urine.
This hormone is the human chorionic gonadotropin hormone – or hCG for short.
Our bodies produce very low levels of hCG, but after the implantation of a fertilised
ovum in the placenta, the concentrations of hCG in a pregnant person’s body dramatically
increases, and this hormone is crucial to signal to the body that it’s time to kickstart
pregnancy.
hCG is what is known as a heterodimeric glycoprotein.
The glycoprotein bit means that it’s a protein with a carbohydrate group attached, and the
heterodimeric part means that it is formed of two different subunits, alpha and beta.
In hCG, the alpha subunit is common to all glycoproteins of the same family, including
follicle-stimulating hormone, luteinising hormone and thyroid stimulating hormone – but
the beta subunit is unique to hCG – and that is precisely what the pregnancy test
strips are designed to detect.
The way pregnancy tests do it is by using a so-called ELISA test, which stands for enzyme-linked
immunosorbent assay.
Its job is to detect a particular substance within a particular liquid, and in this case,
the substance is the unique beta unit from hCG, and the liquid is urine, and it’s a
sandwich because said liquid must pass through three zones lined with antibodies, with the
important test happening in the middle.
Antibodies are very special biological chemicals, made up of a constant zone, and a specific
zone, which is designed to bind to specific compounds.
The first zone is the reaction zone.
It is lined with antibodies that can bind with hCG.
As the urine passes through, these are swept up, and if hCG is present, the antibodies
will bind to it.
The second test zone is lined with antibodies that detect antibodies that are bound to hCG.
These are picked up and cause dye release, which is the positive pregnancy test line
that can be both exciting and terrifying for many!
The final test zone is the control zone, this one simply detects the constant zone of the
passing antibodies to ensure the test has run correctly, and as they detect the antibodies
from the reaction zone passing through, they release dye.
This line basically tells us that the test has run correctly.
Now, so far I’ve spoken about urine tests, which are your traditional over the counter
tests.
However there are also serum tests which take blood, and they can detect even lower concentrations
of hCG, and unlike urine tests which are generally qualitative tests, serum tests can quantify
the levels of hCG.
There are various reasons that you may want to do that.
For one, it can actually tell you exactly when conception happened, but they are informative
in other contexts as well.
For instance, some studies have found links between persistently high levels of hCG in
the first trimester and Down syndrome.
hCG tests are also helpful for detecting and monitoring ectopic pregnancies and miscarriages
and high hCG levels can also be a sign of certain types of tumours and cancer, such
as pituitary gland cancers or testicular cancers, and measuring hormone levels is a very safe
and non-invasive way to monitor them.
Finally, hCG tests can also be used in anti-doping contexts, as some male athletes may use hCG
to stimulate testosterone production due to its similarity to luteinising hormone.
So without a doubt – how much a simple hormone can tell us about the inner workings of our
bodies can be both relieving and mind-boggling – and it’s all thanks to biochemistry!
And hey!
In the time it’s taken me to tell you all of this – my test is ready to interpret!
Negative!
I really hope you enjoyed today's episode - this was actually my entry to the Biochemical
Society's Science Communication Competition back in April aaaand it came in third place
- so I hope you enjoyed it.
if you want to see the first and second entries and I think a few written entries as well,
I will link those down below - and as always, thank you so much for watching me and I'll
see you in the next one!
Bye!
[Music: Thastor & CryoSleepKitten] [Art & Animation: Caro Waro & Cristina de
Manuel] [Hosting, Scripting, Editing: Inés Dawson]
[Translated by {your name} into {language}]