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Thrombosis is the leading cause of death during pregnancy according to new research. Here’s what you need to know

A recent study led by Oxford University has found that the number of women dying during pregnancy and shortly after child birth has increased to levels not seen for twenty years. The results of the study make for stark reading as it found that thrombosis is the leading cause of death in women during pregnancy or within six weeks of their pregnancy ending. Here’s everything you need to know about the condition…

What is thrombosis?

Thrombosis, in simple terms, is a blood clot. Blood clots are typically formed in response to injury or damage to blood vessels, and they play a crucial role in preventing excessive bleeding. However, when a blood clot forms inappropriately within a healthy blood vessel, it can lead to serious health problems.

What can cause it?

There are lots of different factors that can contribute to the development of thrombosis. Here are some key ones to know about:

  • Inactivity or immobility: Prolonged periods of immobility, such as during long flights or bed rest after surgery, can increase the risk of blood clots.
  • Injury to blood vessels: Trauma or surgery can damage blood vessels, triggering the clotting process.
  • Certain medical conditions: Conditions such as atherosclerosis, cancer, and certain genetic disorders can increase the risk of thrombosis.
  • Smoking and obesity: These lifestyle factors can contribute to the development of arterial thrombosis.

Who is at highest risk of thrombosis during pregnancy?

Pregnancy itself is pretty taxing on the body so it’s not surprising that just being pregnant increases your risk of developing a blood clot . This is due to a number of factors such as hormonal changes, increased pressure on blood vessels from the extra weight, and changes in blood composition.

Some women, however, may have additional risk factors that further increase their likelihood of developing thrombosis during pregnancy. These include:

  1. Previous history of thrombosis: Women who have a history of blood clots or thrombosis are at a higher risk during pregnancy. This includes those with a history of deep vein thrombosis (DVT) or pulmonary embolism.
  2. Age: Women who are older than 35 years are generally at a higher risk.
  3. Multiple pregnancies: Women carrying twins or triplets have a higher risk of thrombosis compared to those with a singleton pregnancy.
  4. Obesity: Being overweight or obese increases the risk of thrombosis during pregnancy.
  5. Inherited or acquired blood clotting disorders: Certain genetic factors or acquired conditions that affect blood clotting can increase the risk.
  6. Medical conditions: Pre-existing medical conditions such as lupus, diabetes, and autoimmune disorders can contribute to an increased risk of thrombosis during pregnancy.
  7. Assisted reproductive technologies: Women who undergo fertility treatments, such as in vitro fertilisation (IVF), may have a slightly higher risk.
  8. Prolonged immobility: Bed rest or long periods of immobility due to illness or complications during pregnancy can increase the risk of clot formation.
  9. C-section: Women undergoing a C-section may have a higher risk of thrombosis compared to those who deliver vaginally.

It’s really important to discuss your medical history and any potential risk factors with your midwife and GP. In some cases, preventive measures such as the use of anticoagulant medications or the use of compression stockings may be recommended to reduce your risk of developing a blood clot.

Why is thrombosis dangerous during pregnancy?

Thrombosis during pregnancy can be particularly dangerous due to the potential complications it may cause for both the mother and the developing baby. When a blood clot forms in the wrong way in the body, it can lead to serious consequences:

  • Risk of pulmonary embolism (PE): Thrombosis, particularly deep vein thrombosis (DVT), can lead to the formation of blood clots in the veins. If a clot breaks loose and travels to the lungs, it can cause a pulmonary embolism, a potentially life-threatening condition. PE can compromise the oxygen supply to the body and lead to severe respiratory distress.
  • Risk to the mother’s health: Thrombosis can cause complications for the mother, including organ damage or failure if blood clots interfere with blood flow to vital organs.
  • Risk to the baby: Thrombosis can affect blood circulation in the placenta, reducing the oxygen and nutrient supply to the developing baby. This can result in complications such as restricted growth, delivering early, or stillbirth.
  • Increased risk with C-Section: Women who undergo a C-section ave an increased risk of thrombosis compared to those who deliver vaginally. This is because the surgical procedure itself and the reduced mobility afterwards can contribute to blood clot formation.
  • Recurrence risk in future pregnancies: Women who experience thrombosis during one pregnancy may be at an increased risk of recurrence in subsequent pregnancies.
  • Long-term consequences: Thrombosis can have long-term consequences, including ongoing pain, swelling, and skin changes in the affected limb.

What are the signs and symptoms?

The signs and symptoms of thrombosis during pregnancy can vary depending on the location of the blood clot and the extent of the blockage. It’s important to be aware of these potential symptoms and seek prompt medical attention if they occur:

  • Swelling: Unexplained swelling, particularly in one leg or occasionally both legs, can be a sign of deep vein thrombosis (DVT). The swelling may be accompanied by a feeling of heaviness or discomfort in the affected limb.
  • Pain or tenderness: Pain or tenderness in the affected area, often in the calf, thigh, or pelvis, may be present. The pain may worsen when standing or walking.
  • Red or discoloured skin: The skin over the affected area may appear red or have a bluish tint. This discolouration is often a result of impaired blood flow.
  • Warmth to the touch: The skin over the clot may feel warm to the touch compared to the surrounding areas.
  • Visible veins: In some cases, superficial thrombophlebitis may cause visible redness or inflammation of the veins just beneath the skin’s surface.
  • Shortness of breath: If a blood clot breaks loose and travels to the lungs, it can cause a pulmonary embolism (PE). Symptoms of PE may include sudden shortness of breath, chest pain, and rapid heart rate. Severe cases can lead to fainting or loss of consciousness.
  • Chest pain or discomfort: Chest pain or discomfort, especially when breathing deeply or coughing, may be a sign of pulmonary embolism.
  • Coughing up blood: In rare cases of severe pulmonary embolism, a person may cough up blood or experience bloody sputum.

It’s important to note that some of these symptoms, such as swelling and discomfort, can be common during pregnancy due to hormonal changes and increased fluid retention. However, if you experience any of the above signs or symptoms, especially if they are sudden or severe, it’s crucial to contact your midwife or GP straightaway.

When is thrombosis likely to occur during pregnancy?

The risk of a blood clot is highest during the third trimester, but it can occur at any stage of pregnancy. Here are some key factors that contribute to the increased risk of thrombosis during different stages of pregnancy:

  1. First Trimester: While the risk of thrombosis is generally lower in the first trimester, changes in hormonal levels and increased blood volume may still contribute to a higher risk.
  2. Second Trimester: As the pregnancy progresses into the second trimester, there is an increase in blood volume and hormonal changes. The expanding uterus can also exert pressure on blood vessels, potentially slowing down blood flow and contributing to the risk of thrombosis.
  3. Third Trimester: The third trimester poses the highest risk for thrombosis during pregnancy. The growing uterus puts additional pressure on the pelvic veins and the vena cava, the large vein that returns blood to the heart. This pressure, along with hormonal changes, can increase the risk of deep vein thrombosis (DVT) in the legs.
  4. Labor and Delivery: The process of labor and delivery, especially in the case of a C-Section, can further increase the risk of thrombosis.
  5. Postpartum Period: The risk of thrombosis remains high in the first six weeks after birth. This is partly because the body undergoes so many significant changes after delivery.

Women with pre-existing risk factors for thrombosis, such as a history of blood clots or certain medical conditions, may have an increased risk throughout pregnancy. If you have any of these factors, you should discuss with your midwife and GP as soon as you find out you are pregnant so you can be closely monitored.

What is the treatment?

If you develop a clot during pregnancy, the treatment will vary depending on a few factors. Such has the location of the clot, type of clot and your overall well-being. The main goals of treatment are:

  1. To prevent the clot from growing,
  2. To prevent new clots from forming, and
  3. To reduce the risk of complications.

Some treatment approaches that may be recommended to you include:

  • Anticoagulant Medications: These medications are commonly used to prevent the formation and growth of blood clots. Common anticoagulants include heparin and low molecular weight heparin (LMWH). These medications are often preferred during pregnancy because they do not cross the placenta and have a lower risk of adverse effects on the baby.
  • Compression Stockings: Compression stockings are tight-fitting stockings that help improve blood flow in the legs and reduce the risk of deep vein thrombosis (DVT).
  • Keeping active: Staying physically active and avoiding prolonged periods of not moving is important in preventing blood clots. You’ll likely be encouraged to participate in regular, moderate physical activity.
  • Monitoring: You may be closely monitored through imaging studies, such as ultrasound, to assess the size and location of the clot and to track its response to treatment.
  • Hospitalisation: In severe cases or when there is a risk of complications, hospitalisation may be required. This is especially true if there is a suspicion of a pulmonary embolism (PE) or if your overall condition needs monitoring.

The choice of treatment depends on individual circumstances, and healthcare providers carefully weigh the potential benefits and risks to both the mother and the baby. It’s important to communicate openly with your healthcare team about any concerns, symptoms, or side effects they may be experiencing.

Why are women at risk of thrombosis after birth?

Women are at an increased risk of blood clots after giving birth due to a combination of factors related to pregnancy, delivery, and the postpartum period. The risk is generally highest in the first six weeks after child birth, but it can persist for several weeks. There are several reasons for this increased risk:

  1. Slower blood flow: During pregnancy, there is an increased volume of blood in the circulatory system. After delivery, the sudden reduction in the size of the uterus can lead to a temporary slowdown of blood flow in the veins, especially in the pelvic and lower body veins. This slower blood flow increases the risk of clot formation.
  2. Venous damage during delivery: The physical stress and trauma associated with labour and delivery can cause damage to blood vessels, increasing the likelihood of clot formation.
  3. Increased clotting factors: Pregnancy triggers changes in the blood system to prevent excessive bleeding during childbirth. However, these changes also make the blood more prone to clotting. These alterations in clotting factors can continue in the postpartum period, contributing to an increased risk of blood clots.
  4. C-Section: Women who undergo a C-Section have a higher risk of blood clots compared to those who deliver vaginally. The surgery itself and the associated immobility during recovery contribute to this increased risk.
  5. Dehydration: After delivery, women may experience fluid loss and, in some cases, dehydration, which can contribute to the formation of blood clots.
  6. Immobilisation: During the postpartum period, women may be less mobile, especially if they had a C-Section or experienced complications during delivery. Prolonged periods of immobility can increase the risk of blood clots.
  7. Pre-existing conditions: Women with pre-existing risk factors for blood clots, such as a history of thrombosis, clotting disorders, or obesity, may be at a higher risk after giving birth.

To reduce the risk of postpartum blood clots, midwives and doctors often suggest the following measures to help keep blood flowing well:

  • Early movement and encouragement of physical activity after delivery.
  • Compression stockings to improve blood circulation.
  • Administration of anticoagulant medications (blood thinners) in certain high-risk cases, especially for women who have undergone a C-Section or have additional risk factors.

What is the difference between thrombosis and thromboembolism?

Thrombosis and thromboembolism are two terms which relate to the different stages of the blood clot process. In simple terms, thrombosis refers specifically to the formation of blood clots within blood vessels. Whereas thromboembolism is a wider term that includes the detachment of a clot (embolus) and its movement through the bloodstream, potentially causing obstruction in other vessels.

What else did the research find?

In addition to identifying thrombosis and thromboembolism as causing higher rates of maternal deaths, the study also found that other leading causes include COVID-19, heart disease and mental health problems. The study also found that the maternal death rate for women from Black ethnic backgrounds has decreased slightly from the rate in 2019-21 but Black women remain three times more likely to die compared to White women. The maternal death rate for women from Asian ethnic backgrounds remains two times higher than that of White women. Women living in the most deprived areas still have a maternal death rate more than twice that of women living in the least deprived areas.

Professor Marian Knight, Director of the National Perinatal Epidemiology Unit and MBRRACE-UK maternal reporting lead, said: ‘These data show that the UK maternal death rate has returned to levels that we have not seen for the past 20 years. The 2023 MBRRACE-UK maternal confidential enquiry report identified clear examples of maternity systems under pressure and this increase in maternal mortality raises further concern. Ensuring pre-pregnancy health, including tackling conditions such as overweight and obesity, as well as critical actions to work towards more inclusive and personalised care, need to be prioritised as a matter of urgency now more than ever.’

Dr Nicola Vousden, Co-Chair of the Faculty of Public Health Women’s Health Specialist Interest Group, said: ‘Persisting inequalities by ethnicity and socioeconomic status indicate that we must think beyond maternity care to address the underlying structures that impact health before, during and after pregnancy, such as housing, education and access to healthy environments.’

Thrombosis Symptoms Checklist

Remember, if you’re ever worried about something during pregnancy, get in touch with your midwife straightaway to discuss your concerns. As a helpful reminder, here’s a little checklist of thrombosis symptoms to know about. And if you know a babe who would benefit from knowing about these symptoms too, feel free to share…


Birthbabe does not provide medical advice, diagnosis, or treatment. The resources on our website are provided for informational purposes only. You should always consult with a healthcare professional regarding any medical diagnoses or treatment options.

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