With the news that the AstraZeneca and Johnson & Johnson vaccines are being linked to an increased risk of a rare type of blood clot, we want to make sure you understand the real chances of developing a blood clot and the reasons why, so that you can make more informed decisions about your healthcare.
Blood clots can be caused by many different things, and although they are incredibly rare, risk factors such as smoking, a high BMI, high blood pressure, migraines, a family history of clotting, recent surgery, and pregnancy can make you more likely to develop a blood clot.
There are also certain medications, such as the contraceptive pill, that can make you more likely to get them. However, the benefits of most medications, like the pill, tend to greatly outweigh the risks of negative side effects. So, while these side effects are always detailed, the chances of them actually happening are small and you shouldn’t make any sudden changes to your medications or lifestyle without consulting your doctor first.
It's also important to remember that before prescribing any medication your doctor will review your medical history and make sure it's safe for you to take.
Read on to learn more about blood clots, the risks and most common causes.
What are blood clots?
Blood clots are gel-like clumps of blood which are usually created in response to a cut or injury. These clots help to slow down bleeding and to try to repair the damage. These types of clots are not a problem, and are actually a very vital part of the healing process. Eventually, these blood clots dissolve.
However, blood clots can also form without an appropriate trigger, which can cause problems. These clots can stay in the same place (called a thrombosis) or move around the body (called an embolism or thromboembolism). Immobile clots typically don’t cause problems, but if a clot starts to travel around the body then it can be dangerous.
If this happens, you may experience symptoms like shortness of breath, chest pain and light-headedness. Left untreated, blood clots can cause more serious health complications, such as strokes. So, if you’re concerned you may have a blood clot or are experiencing the symptoms of a blood clot, you should seek immediate medical advice.
Blood clots and the contraceptive pill
The contraceptive pill, like all medicines, comes with a risk of side effects. Blood clots are a known side effect of contraceptive pills, though they are very rare - only affecting 2 in 10,000 women. Most contraceptive pills also require a prescription from a doctor before you can start taking it. This is to make sure that the pill is safe for you, and that you understand the risks of side effects before you start taking the pill. If your doctor does identify a risk, they will recommend an alternative pill or form of contraception.
What is the likelihood of getting a blood clot while on the pill?
To better understand the chances of developing a blood clot while taking the contraceptive pill, it’s essential to look at the data to put things in perspective. Right now, it’s estimated that:
- 2 out of 10,000 (.02%) women who are not on the combined pill or pregnant, will get a blood clot in the legs or lungs per year.
- 6 out of 10,000 (.06%) women who use a combined pill that contains levonorgestrel, will develop a blood clot within a year.
The contraceptive pill triples the likelihood of getting a blood clot, which can be quite an alarming number to hear. However, the overall risk of you developing a blood clot while taking the contraceptive pill is roughly 0.06%, which is still incredibly low.
To put this into perspective, your chance of developing a blood clot on a long-haul flight is roughly 2-6% depending on your personal circumstances and the length of your journey - up to 100 times higher than taking the pill. And, while you may not fly as regularly as you take the contraceptive pill, it’s a risk that most people are happy to take to enjoy travel.
If you are worried about developing a blood clot, you should speak to your GP. You should also learn the signs and symptoms of a blood clot so that you can take appropriate action quickly if you need to.
Blood clots and pregnancy
Pregnancy increases your risk of developing blood clots, but it is still a very rare occurrence. And, while women are up to 5-10 times more likely to develop a blood clot when pregnant compared to when they’re not, there is still very little chance of this actually happening.
When you look at the data, you can see that:
This means that there is a 0.05% - 0.2% chance of developing a blood clot while pregnant and a slightly higher chance in the period shortly after giving birth. Knowing the risks, we can still make the informed decision to have children if the benefits outweigh the risk. And, unless you have a condition making you more likely to develop a clot, it’s unlikely that the risks associated with it will stop you from wanting to become pregnant.
- Out of every 10,000 pregnant women, 5 to 20 of them will develop a blood clot.
- Out of every 10,000 women in the first 12 weeks after giving birth, 40 to 65 of them will develop a blood clot.
Obesity and blood clots
Both men and women are at an increased risk of developing blood clots if they are obese. This risk increases with age, as people over 50 who are obese are twice as likely as younger people to get a blood clot. The extent of obesity also increases the likelihood of blood clots developing, meaning the more obese you are, the more likely you are to develop a blood clot.
However, when you look at the data, women only have a 0.2% chance of developing a blood clot due to obesity, which is also drastically lower than the risk you would take on a long-haul flight. That’s not to say that you shouldn’t be concerned about the risks of obesity, and you should still speak to your doctor and work on a plan to maintain a healthy BMI. That’s because while blood clots may not be a huge risk factor caused by obesity, there are many other aspects of obesity that negatively impact your health and well being.
Blood clots and smoking
Studies have shown that smoking increases the risk of blood clots in the lungs or legs. This risk also increases if you have other risk factors such as heart problems.
Recent research conducted between 1996 and 2013 looking into a particular type of blood clot, common in smokers, found that:
- People who smoke have a 17% higher risk of developing a deep vein blood clot compared with people who have never smoked.
- Current smokers are 23% more likely to develop a deep vein blood clot compared with those who have never smoked.
- Former smokers are 10% more likely to experience a deep vein blood clot compared with people who have never smoked.
However, this risk significantly increases if you have a high BMI or if you smoke while taking the pill. Due to this, if you are a smoker, some pills may not be safe for you to take - especially combined contraceptive pills. You should let your doctor know if you smoke before starting the contraceptive pill.
This doesn’t mean that smoking is ‘less dangerous’ than taking the contraceptive pill. While smoking may not lead to a large risk of blood clots, it can lead to many more serious health conditions.
We provide a quit smoking service to help you break the habit and lead a healthier life.
Blood clots and surgery
When you undergo surgery, there is always an increased risk of developing a blood clot. This can happen during the surgery itself, but is more likely to be caused by inactivity during recovery. This risk increases during the first 12 weeks following your operation, but the likelihood also depends on the type of surgery and your medical background. For example:
No surgery is risk-free, but in most cases the benefits of surgery greatly outweigh the risks of developing blood clots. Some patients are also given blood thinning medications to help reduce the risk of developing blood clots after their operation.
- Approximately 1 in 45 people will develop a blood clot after a hip or knee replacement surgery
- An estimated 1 in 85 people will develop a blood clot after cancer surgery
- Only 1 in 815 people will be likely to develop a blood clot after a standard day surgery that doesn’t involve an overnight stay.
While the thought of surgery can be scary, you should not put it off for fear of developing a blood clot. You are far more likely to develop a severe problem from ignoring an issue than you are to develop a blood clot because of it, unless a doctor has told you otherwise.