Postpartum deep vein thrombosis (DVT): risk, symptoms and treatment

The RCOG defines a DVT as a blood clot that forms in a deep vein of the leg, calf or pelvis. Pregnancy increases the risk, with the highest risk being just after you have had your baby, yet it is still uncommon at 1 to 2 in 1,000 women in pregnancy and the first 6 weeks afterwards. The NHS includes pregnancy and the first 6 weeks after having a baby among times with a higher chance of DVT.

The RCOG says DVT matters because the clot may break off and lodge in the lung, causing a pulmonary embolism, and that diagnosing and treating a DVT reduces the risk of this. A separate guide on pulmonary embolism after birth covers the lung symptoms in detail.

The RCOG lists factors that add to your risk after the birth: a very long labour (more than 24 hours) or a caesarean section, losing a lot of blood or receiving a transfusion. Other listed factors include being over 35, having had three or more babies, a previous venous thrombosis or one in a close relative, thrombophilia, certain medical conditions, painful or large varicose veins, using a wheelchair, a BMI over 30, smoking, admission to hospital, a multiple pregnancy, dehydration or long immobility (such as after an operation or a journey of 4 hours or more), and pre-eclampsia.

The RCOG says your midwife should carry out a risk assessment at booking and at about 28 weeks, if circumstances change, and after the baby is born, to decide whether you would benefit from preventive treatment. Some risk factors, like a previous thrombosis, are enough on their own for treatment to be recommended. The NHS adds that an assisted birth carries a higher chance of blood clots in the veins of the legs or pelvis, which can be reduced by moving around as much as you can and may involve anti-clot stockings and heparin.

The NHS says DVT symptoms include throbbing pain in one leg (rarely both), usually in the calf or thigh, swelling in one leg, red, blue or darkened skin (which can be harder to see on brown or black skin), and swollen veins. The NHS "your body after the birth" page lists pain, swelling or redness in one calf as a symptom to tell your midwife, health visitor or GP about straight away. The NHS says sometimes the only symptom is pain in the lower tummy, which is a rare pelvic vein thrombosis.

The RCOG says swelling and discomfort in both legs is common in pregnancy and does not always mean a problem, and to ask your doctor or midwife if worried. After the birth, the NHS advises an urgent GP appointment or NHS 111 if you think you have DVT, and to call 999 or go to A&E if you also feel short of breath or have chest pain; do not drive yourself.

If you have symptoms the RCOG says your doctor will examine the leg and may recommend an ultrasound scan to look for the clot; if nothing is seen but symptoms continue, the scan may be repeated a few days later. The NHS says that if a doctor thinks you have DVT you should be referred to hospital within 24 hours for an ultrasound scan, which shows whether blood is flowing normally through the vein.

The RCOG says that if a venous thrombosis is suspected you will be advised to start heparin injections to thin the blood, most commonly low-molecular-weight heparin, which does not cross the placenta. It works to stop the clot growing so the body can gradually dissolve it, reduces the risk of a PE and another thrombosis, and lowers long-term leg problems. It is given as a daily injection under the skin (sometimes twice daily); you or a family member are shown how, and needles and syringes are provided. About 1 to 2 in 100 have an allergic reaction, so report a rash. Bruising at the injection site usually fades in a few days.

Treatment is usually recommended for the remainder of pregnancy and for at least 6 weeks after the birth, with a minimum of 3 months, and longer if the clot was diagnosed late or after birth. After birth there is a choice between continuing heparin injections or warfarin tablets, which your doctor discusses. The NHS describes blood-thinning injections for the rest of pregnancy and until the baby is 6 weeks old if DVT occurs in pregnancy. A special graduated compression stocking may be prescribed to ease swelling. Never stop or adjust anticoagulant treatment without medical advice.

The RCOG says you will usually be given an appointment with your GP, obstetrician or haematologist to ask about family history, discuss tests for thrombophilia (best done after stopping treatment and ideally before a future pregnancy), and talk about contraception. It advises not taking contraception that contains oestrogen, such as the combined pill. In a future pregnancy, heparin is usually recommended during and after it. NHS advice for recovery after DVT includes staying active, raising the leg when sitting, and delaying flights or long journeys until at least 2 weeks after starting blood thinners. Prevention steps differ for each person, so rely on your own risk assessment.