Deep vein thrombosis in pregnancy: symptoms, risk and treatment

A thrombosis is a blood clot in a blood vessel. RCOG explains that a deep vein thrombosis is a clot that forms in a deep vein of the leg, calf or pelvis. Veins carry blood back towards the heart and lungs.

The NHS adds that DVT is more likely in people who are pregnant or have had a baby in the previous 6 weeks, and in those who are pregnant and have had DVT before. It describes DVT as dangerous because clots can travel to the lungs, which is called a pulmonary embolism.

RCOG stresses that although pregnancy increases the risk, dying from a pulmonary embolism is very rare in women who are pregnant or who have just had a baby, and that diagnosing and treating a DVT reduces the risk of developing one.

RCOG says the symptoms of a DVT usually occur in only one leg. It recommends seeking advice immediately from your doctor or midwife if you notice any of the following.

• A red and hot swollen leg.

• Swelling of your entire leg or just part of it, or it may just feel heavy.

• Pain or tenderness, which you may only experience when standing or walking.

• The NHS adds throbbing pain in one leg, usually in the calf or thigh, and red, blue or darkened skin; sometimes the only symptom is pain in the lower tummy, which can be a sign of pelvic vein thrombosis.

The NHS says to ask for an urgent GP appointment or get help from NHS 111 if you think you have DVT, and that if you are pregnant you can also call an early pregnancy unit if you are less than 20 weeks, or your maternity unit.

Call 999 or go to A&E if you have symptoms of DVT and feel short of breath or have chest pain, because the clot may have travelled to the lungs. RCOG lists sudden unexplained difficulty in breathing, tightness in the chest or chest pain, coughing up blood, and feeling very unwell or collapsing as symptoms of a pulmonary embolism. The NHS says not to drive to A&E: ask someone to drive you or call 999.

Because swelling in both legs is common in pregnancy, RCOG advises asking your doctor or midwife if you are worried, rather than assuming either way.

RCOG lists risk factors before pregnancy: being over 35, having had three or more babies, a previous venous thrombosis, a close relative who has had one, a thrombophilia, a medical condition such as heart or lung disease, severe varicose veins, or being a wheelchair user. Lifestyle factors include a BMI over 30, smoking and intravenous drug use.

During pregnancy, it lists hospital admission, multiple pregnancy, dehydration or reduced mobility such as from vomiting or severe infection, being immobile for long periods including travelling for 4 hours or longer, and pre-eclampsia. After the birth, risks include a very long labour of more than 24 hours, a caesarean section, heavy blood loss or a blood transfusion.

RCOG says you should have a risk assessment during pregnancy and after your baby is born, so that your doctor or midwife can decide whether you would benefit from preventive treatment.

RCOG says that if you have symptoms, your doctor will examine your leg and may recommend an ultrasound scan to see whether there is a thrombosis. If none is seen but you are still having symptoms, the scan may be repeated a few days later. The NHS says a doctor who suspects DVT should refer you to hospital within 24 hours for an ultrasound scan.

For a suspected pulmonary embolism, RCOG lists tests that may include a chest X-ray, a CT scan of the lungs, a VQ scan and an ultrasound of both legs. It explains that the scans use radiation, that the chest X-ray dose is tiny, and that the small risk of CT and VQ scans must be weighed against the risk of an undiagnosed pulmonary embolism, with the doctor explaining the benefits and risks.

RCOG says that if your doctor suspects a venous thrombosis you will be advised to start treatment with an injection of heparin, 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 pulmonary embolism and another thrombosis, and lowers the risk of long-term leg problems.

RCOG says after the birth treatment should continue for at least 6 weeks, with a choice of continuing heparin injections or warfarin tablets, and that both heparin and warfarin are safe when breastfeeding.

After birth you will usually have an appointment with your GP, obstetrician or haematologist, to discuss family history, tests for thrombophilia once treatment is stopped, contraception, and future pregnancies. RCOG says you should be advised not to take contraception that contains oestrogen, such as the combined pill, and that you will usually be recommended heparin during and after your next pregnancy.

On the NHS, risk assessment is part of routine antenatal care and a suspected DVT is assessed through maternity services, early pregnancy units or A&E, with ultrasound within 24 hours and heparin treatment started promptly.

Private obstetric care follows the same guidance. For anyone with a history of clots or thrombophilia, early review by an obstetrician or haematologist who specialises in thrombosis in pregnancy, which the NHS GP can arrange, is the key step whichever route is chosen.