Pulmonary embolism in pregnancy and after birth: symptoms, tests and treatment

The NHS describes a pulmonary embolism as a blood clot that blocks a blood vessel in the lungs, which can be life-threatening if not treated quickly. It often happens when part of a clot in the leg, called a deep vein thrombosis (DVT), breaks off and travels to the lungs.

The RCOG explains that a DVT is a clot in a deep vein of the leg, calf or pelvis, and that when a clot breaks off and lodges elsewhere, such as the lung, it is a pulmonary embolism. Diagnosing and treating a DVT reduces the risk of developing a PE. In pregnancy a DVT can occur at any time, including the first 3 months, which is why the RCOG advises seeing a midwife early.

The RCOG describes DVT symptoms as usually affecting only one leg: a red, hot, swollen leg, swelling of the whole leg or part of it, or a heavy feeling, and pain or tenderness that may only be felt when standing or walking. It points out that swelling and discomfort in both legs is common in pregnancy and does not always mean there is a problem, so ask your midwife or doctor if you are worried.

For a pulmonary embolism, the RCOG lists sudden unexplained difficulty in breathing, tightness in the chest or chest pain, coughing up blood and feeling very unwell or collapsing. The NHS lists difficulty breathing that comes on suddenly, chest pain that is worse when you breathe in and coughing up blood. It says to ask for an urgent GP appointment or get help from NHS 111 if you have sudden difficulty breathing or are coughing up blood, and to call 999 or go to A&E if you have severe difficulty breathing, pain in your chest or upper back, a very fast heartbeat or someone has passed out. It advises not to drive to A&E yourself.

• One leg red, hot, swollen or tender, particularly if only one side is affected.

• Sudden breathlessness that has no clear explanation.

• Chest pain or tightness, or pain that is worse on breathing in.

• Coughing up blood.

• Feeling very unwell or collapsing: call 999.

The RCOG lists risk factors that may be present before pregnancy: being over 35, having had three or more babies, a previous venous thrombosis, a close relative with venous thrombosis, a thrombophilia (a condition that makes clots more likely), medical conditions such as heart or lung disease or arthritis, severe painful varicose veins and being a wheelchair user. Lifestyle factors include a body mass index over 30, smoking and intravenous drug use.

During pregnancy it lists hospital admission, a multiple pregnancy, dehydration or reduced mobility from severe vomiting, infection or fertility-treatment complications, long periods of immobility including travelling for 4 hours or longer, and pre-eclampsia. After birth, risk factors include a labour of more than 24 hours or a caesarean section, heavy blood loss and blood transfusion.

The RCOG says most DVTs and PEs in pregnancy and after birth are preventable. A risk assessment should be done at the first antenatal booking, around 28 weeks, if circumstances change or you are admitted to hospital, and after the baby is born. Some risk factors, such as a previous clot, are enough on their own for preventive treatment to be recommended.

The RCOG says that for a suspected DVT the doctor will examine your leg and may recommend an ultrasound scan, repeated a few days later if no clot is seen but symptoms continue. For a suspected PE, tests may include a chest X-ray, a CT scan of the lungs, a VQ scan, which involves a drip in the arm, and an ultrasound of both legs if there are DVT symptoms.

The RCOG explains that the chest X-ray uses a tiny dose of radiation that is not considered harmful to you or your baby, and that CT and VQ scans carry a small risk that needs to be weighed against the risk of an undiagnosed PE. The risk to the baby of developing childhood cancer after either scan is extremely low, although slightly higher with a VQ scan, while a CT scan gives a higher radiation dose to the breasts. Your doctor will talk through which test is best for you.

The NHS says that at hospital you will probably be given an injection of anticoagulant medicine before test results are available.

The RCOG says that if a venous thrombosis is suspected you will be advised to start an injection of heparin to thin the blood, most commonly low-molecular-weight heparin in pregnancy. It works to prevent the clot getting bigger so the body can gradually dissolve it, reduces the risk of a PE and of another thrombosis, and lowers the risk of long-term leg problems. The injection is given under the skin at the same time every day, sometimes twice daily, with the dose based on your weight in early pregnancy, and you or a family member will be shown how to give it.

Low-molecular-weight heparin does not cross the placenta and cannot harm the baby. Bruising at the injection site usually fades in a few days, and 1 to 2 in 100 women have an allergic reaction, in which case the heparin type can be changed. Treatment is usually recommended for the rest of the pregnancy and for at least 6 weeks after birth, with a minimum of 3 months. You will usually be prescribed a graduated compression stocking to reduce leg swelling and be encouraged to stay active.

The RCOG advises that if you think you are going into labour you should not have any more injections and should phone your maternity unit, telling them you are on heparin. An epidural cannot be given until 24 hours after your last heparin injection, and alternative pain relief is available. If labour is induced, injections should stop 24 hours before. For a planned caesarean the last injection should be 24 hours before, with heparin usually restarted within 4 hours of the operation. If an emergency caesarean is needed within 24 hours of the last injection, a general anaesthetic rather than a spinal or epidural may be needed.

After the birth, treatment continues for at least 6 weeks, with a choice between continuing heparin injections or warfarin tablets, and longer if the clot was diagnosed late in pregnancy or after birth. The RCOG says both are safe when breastfeeding. A follow-up appointment will usually cover family history, tests for thrombophilia after treatment has stopped, contraception, where the RCOG advises against contraception containing estrogen such as the combined pill, and future pregnancies, when heparin treatment is usually recommended.

In the UK, suspected PE in pregnancy is an emergency pathway handled through maternity services, emergency departments and a haematology or obstetric medicine team, all within the NHS. Some women choose private obstetric or haematology care for planning future pregnancies after a clot. Whichever route is used, make sure the team knows about any past clot, thrombophilia result or medicine such as warfarin before you conceive, as the RCOG explains that warfarin may need to be changed to heparin.