Can pregnancy increase the risk of pulmonary embolism? 

Pregnancy is a significant physiological event that causes various changes in the body, including alterations in how the blood clots. These natural changes are designed to protect the mother from excessive bleeding during childbirth, but they also result in a higher risk of developing blood clots in the veins. Understanding why this happens and how healthcare professionals in the UK monitor and manage these risks is essential for ensuring a safe pregnancy and postpartum period. 

What We’ll Discuss in This Article 

• Why pregnancy naturally increases the likelihood of blood clots. 

• The physical and hormonal changes that affect blood circulation. 

• Identifying specific risk factors that further increase the danger. 

• How the NHS assesses and monitors risk throughout pregnancy. 

• Preventative measures used to protect women and their babies. 

• Recognising emergency symptoms that require immediate medical attention. 

Why does pregnancy increase the risk of blood clots? 

Pregnancy increases the risk of pulmonary embolism because the blood naturally becomes “stickier” and more prone to clotting to prevent heavy bleeding during and after delivery. The NHS states that the risk of a blood clot is higher in pregnancy because of changes in the blood, and this risk continues for up to six weeks after the baby is born. Additionally, the growing uterus can put physical pressure on the veins in the pelvis, which slows down the flow of blood from the legs back toward the heart, potentially leading to a clot. 

Physiological changes affecting circulation 

During pregnancy, high levels of hormones like oestrogen cause the body to produce more clotting factors and fewer anti-clotting proteins. This shift in blood chemistry occurs alongside a significant increase in total blood volume, which can cause the veins to dilate and the blood flow to become more sluggish. These factors combined create an environment where a clot is more likely to form in the deep veins of the leg, known as deep vein thrombosis, which can then travel to the lungs to cause a pulmonary embolism. 

Identifying high risk factors in pregnancy 

While all pregnant women are at a slightly higher risk of clots than those who are not pregnant, certain factors can make some individuals much more susceptible. Women who are over the age of 35, those who are obese, or those who have a personal or family history of blood clots are considered to be in a higher risk category. NICE clinical guidelines recommend that healthcare professionals assess every pregnant woman for venous thromboembolism risk at their first booking appointment and again if they are admitted to the hospital. 

Risk Factor	Reason for Concern
Age over 35	Natural changes in vascular health and circulation.
Obesity (BMI >30)	Increased physical pressure on pelvic and leg veins.
Multiple Pregnancy	Larger uterus causes more significant venous obstruction.
Recent Surgery	Clotting risks are heightened during post-operative healing.
Reduced Mobility	Prolonged bed rest or travel prevents healthy blood flow.

Managing and monitoring risk throughout pregnancy 

In the UK, the risk of a pulmonary embolism is managed through regular clinical assessments during antenatal and postnatal visits. If a woman is identified as being at high risk, she may be prescribed preventative treatment such as daily injections of low molecular weight heparin. This medication is safe for both the mother and the baby and works to lower the blood’s clotting ability without crossing the placenta. Clinical teams also provide advice on staying active and well-hydrated to support healthy circulation. 

Preventative measures for pregnant women 

Beyond medication, there are several simple steps that can be taken to reduce the risk of a blood clot during and after pregnancy. Regular gentle exercise, such as walking, helps to keep the blood moving through the veins, while avoiding long periods of sitting or standing still is equally important. For those at moderate risk, midwives or doctors may also recommend wearing graduated compression stockings, which apply gentle pressure to the legs to help the blood flow back toward the heart more efficiently. 

Conclusion 

Pregnancy naturally increases the risk of pulmonary embolism due to hormonal and physical changes that affect how the blood clots and flows. While the absolute risk remains low for most women, the NHS and NICE have strict protocols in place to identify and protect those at higher risk through regular assessment and preventative care. Staying informed about the symptoms of a clot is a vital part of ensuring a safe and healthy pregnancy experience. If you experience severe, sudden, or worsening symptoms, call 999 immediately. 

Authority Snapshot (E-E-A-T Block) 

This guide was produced by the MyPatientAdvice Medical Content Team and reviewed by Dr. Stefan Petrov to provide safe, evidence-based health information for pregnant women. The content is strictly aligned with the official clinical standards and preventative guidance provided by the NHS and NICE regarding venous thromboembolism in pregnancy. Our purpose is to educate the public on standard UK medical assessments and the importance of professional monitoring to ensure maternal and foetal health.