Freshly Baked Science

red blood cells close up in the human body platelets flowing through arteries blood clot black and white with colour

I've Been Through A Clot

4th June 2018

Blood is an essential part of daily life, making up around 7-8% of our total body weight (that explains the number on the scales!). Our blood spends all day, every day, doing laps of our body, delivering oxygen and nutrients along the way and picking up carbon dioxide and other nasty waste products. On top of all that, it is also responsible for fighting off any foreign invaders and keeping your body at a constant temperature. Not bad for a days work, right?


Our blood is made up of over 4,000 different components, including red blood cells, white blood cells, platelets and plasma. For the sake of this post, we are going to be focusing on platelets and plasma. Platelets are responsible for sticking together in response to an injury. They plug up a wound and prevent us bleeding to death (always useful). In order to carry this out, it needs some help from a group of 13 different proteins in the plasma called clotting factors.


Although this natural process is usually very useful for us, it can occasionally occur without a wound as a trigger. This abnormal clotting results in the formation of a clot inside a vein or artery. If the clot is big enough, it creates a 'roadblock', preventing normal blood circulation. This has the potential to lead to one of three life-threatening conditions:


1 Heart Attack– a blood clot in an artery leading to the heart.

2 Stroke– a blood clot blocking passage to the brain.

3 Pulmonary Embolism– a blood clot blocking an artery in the lung.


These conditions can be extremely serious: causing around 544,000 deaths per year in Europe, which is more than AIDS, breast cancer, prostate cancer and car crashes combined!


So, why might a clot develop?


A major factor increasing the risk of blood clots is the contraceptive pill. This is the leading form of contraception (birth control), yet there are an alarming amount of people taking this, without being aware of the risks. While the contraceptive pill doesn’t cause blood clots;  it can increase the risk by 3-4 times, and is even higher in smokers, or those with a family history of blood clots.


What is the contraceptive pill?


The combined contraceptive pill contains 2 hormones: oestrogen and a synthetic progesterone. These hormones are naturally produced during pregnancy, to keep a baby in the womb until birth. By taking the contraceptive pill, the body is fooled into thinking it is pregnant, therefore preventing any ‘further‘ pregnancy.


How does the Pill encourage clotting?


The oestrogen in these pills also has the ability to increase the amount of clotting factor in the blood plasma. It does this by entering a cell, and causing a chain reaction: eventually resulting in the cell being instructed to make more clotting factors (essentially a protein photocopier).


The clotting factors we are going to focus on are called: factor V, factor VII, factor VIII and factor S (thank you science for keeping the names simple!). Oestrogen causes factor VII to increase the most, whereas there is actually a decrease in factor V. This may seem like a benefit: however factor V and factor S actually work together to stop the production of factor VIII (i.e. more factor VIII is produced in the absence of factor V), therefore the benefit is neutralised. 


If you picture clot formation and clot breakdown on either side of a weighing scale, in normal conditions this would be balanced. When there are high levels of oestrogen present, it adds extra weight to the clot formation side, therefore encouraging platelets to stick together.


Time for a change?


The common risk assessment for clotting on the contraceptive pill is simply to determine if there is a family or personal history of clots, and checking if a person smokes. However, a recent study of 87 women who experienced a clot showed the following stats:


• 95% weren’t smoking at the time; 78% had never smoked

• 58% had no family history of clots

• 80% didn’t have a known disorder

• 75% developed a clot, after more than a year taking the contraceptive pill

• Only 2% were tested for a disorder, after the identification of a family history


These stats question all current procedures for clot prevention, which may warrant for a change of strategy, and fast!


Wishing you all good health and happiness, and remember to B positive (sorry- pun alert).


We would love to hear your thoughts on the contraceptive pill! Email us at, or tweet us (@magazinewonk) with the hashtag #letstalkcontraceptive

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