The likelihood of blood clots forming in veins – venous thromboembolism – increases in pregnancy.

BLOOD travels from the heart to the rest of the body through blood vessels called arteries, and returns back to the heart through other blood vessels called veins.

Veins are either superficial or deep. The former are close to the surface of the body, and the latter are deep in the body and are almost always beside an artery of the same name, eg the iliac vein is adjacent to the iliac artery.

Arteries and veins are structurally different. The former have muscular walls, unlike the latter, which also contain valves.

The term venous thromboembolism (VTE) is used to refer to blood clots forming in veins. VTE can occur in any vein in the body, and a common site is the veins in the legs.

Blood clots can form in an artery or a vein (thrombosis). Arterial thrombosis leads to a compromise of the blood flow to the body part served by the artery.

The term venous thromboembolism (VTE) is used to refer to thrombosis in veins. VTE can occur in any vein in the body. The common sites are the veins in the legs and/or pelvis (leading to deep vein thrombosis – DVT) and the lungs (leading to a pulmonary embolism – PE).

The most serious complication of a DVT is PE, which is life-threatening. PE results from a thrombus breaking off (embolising) and travelling to the lungs where it can get stuck, leading to a compromise in the blood flow to the affected part of the lungs.

The likelihood of DVT is increased during pregnancy, and in the first six weeks after childbirth. The risk is one in 500, which is 10 times the risk of a non-pregnant woman of the same age.

The highest risk of DVT and/or PE is in the immediate period after childbirth. However, it is important to remember that DVT and/or PE can occur at any time during pregnancy, even in the first three months.

About 10 to 20% of VTEs are PEs, which is a common cause of maternal deaths in developed and developing countries, including Malaysia.

Defining risk factors

There are several risk factors, some of which are inherited, while others are acquired. These risk factors are identifiable in about 80% of those affected. It is not uncommon for a person to have more than one risk factor.

The inherited risk factors include Factor V Leiden mutation, Prothrombin gene G20210A mutation, Antithrombin III deficiency, Protein C or S deficiency, disorders of plasminogen and plasminogen activation, and a strong family history (mother, father, brother or sister who has had a DVT).

The acquired risk factors include obesity (body mass index, BMI, of 30 kg/m² or more), smoking, intravenous drug usage, immobilisation (more than four days of bed rest), previous thrombosis, trauma, cancer, infections, nephrotic syndrome, cerebrovascular event, severe varicose veins, especially if they are painful, and long-haul travel of four hours or more.

A pulmonary embolism results from a thrombus breaking off (embolising) and travelling to the lungs where it can get stuck, leading to a compromise in the blood flow to the affected part of the lungs.

The risk factors related to pregnancy are maternal age of 35 years or more, multiparity (have had three or more babies), previous DVT, high blood pressure, dehydration, medical conditions like heart disease, lung disease or arthritis, multiple pregnancy (twins or more), and hospitalisation.

The risk factors related to delivery are prolonged labour, instrumental vaginal delivery, Caesarean section, post-partum haemorrhage, and blood transfusion.

The risk of VTE may increase or decrease. It may increase if other factors develop in addition to the initial risk factors, eg complications during delivery in an obese mother. It may decrease with smoking cessation.

The obstetrician and the midwife will assess a pregnant woman’s risk at the time of pregnancy, when changes occur during pregnancy, at admission to hospital, and after delivery.

The clinical features of DVT and PE are the same as that of the non-pregnant.

The features of DVT include discomfort and/or pain in the legs, swelling, tenderness, warmth, and an increased white blood cell count. There may be abdominal pain. Some of these symptoms are non-specific as they are also found in normal pregnancies.

There may be no symptoms in about 50% of those with DVT.

The features of PE include sudden unexplained difficulty in breathing, tightness in the chest or chest pain, coughing up blood (haemoptysis), and collapse. There may be no symptoms in some patients.

Diagnosis and treatment

DVT is diagnosed clinically and with an ultrasound scan of the leg. If there is no sign of thrombosis but the symptoms persist, a repeat ultrasound is usually done.

PE is diagnosed with a chest X-ray, a CT scan of the lungs, and/or a ventilation perfusion (VQ) scan of the lungs. The amount of radiation in a chest X-ray is very small. If it is done during pregnancy, the foetus will be protected with a shield.

There are small radiation risks from CT and VQ scans, which have to be balanced with the risks to the mother and foetus of an undiagnosed PE.

The risk of developing childhood cancer from a CT scan is less than one in 1,000,000, and one in 280,000 with a VQ scan. However, the radiation dose to the breast from a CT scan is more than that of a VQ scan, which may increase the lifetime risk of breast cancer.

After a diagnosis of DVT has been made, the patient will be prescribed an anticoagulant called heparin to “thin the blood”. The heparin prevents the thrombus from increasing in size so that it can dissolve gradually, reducing the risk of the development of another thrombus, thus reducing the risk of PE.

There are different types of heparin, with “low molecular weight heparin” (LMWH) commonly prescribed in pregnancy. It is given as an injection underneath the skin (subcutaneous) at the same time every day, and sometimes, twice daily. The dose is adjusted according to body weight.

Patients will be taught how and where to inject themselves, just like diabetics with insulin injections.

Hospitalisation is usually not required with most mothers managed as out-patients. The heparin has to be injected for the rest of the pregnancy.

LMWH does not harm the foetus because it does not cross the placenta. There may be some bruising at the injection site, which usually fades away within a few days. An allergic reaction may occur in one to two in every 100 women.

If there is a rash after the injection, the doctor should be informed, and the type of heparin changed.

Heparin has to be stopped when labour is suspected to have started. It is stopped 24 hours before induction of labour or planned Caesarean section.

Epidural analgesia or anaesthesia cannot be given until 24 hours after the last heparin injection. An alternative mode of pain relief will be recommended.

Heparin will usually be recommenced about four hours after a planned Caesarean section. If an unplanned (emergency) Caesarean section is indicated within 24 hours of the last heparin injection, it will be done under general anaesthesia, and not epidural or spinal anaesthesia.

Anticoagulants will be prescribed for at least six weeks after childbirth. The choices of continuation of heparin injections or warfarin tablets should be discussed with the obstetrician.

Both heparin and warfarin can be taken by breastfeeding mothers.

Warfarin is not prescribed in pregnancy as it can harm the foetus. So, a pregnant mother on warfarin would be advised to stop it and take heparin instead.

Other therapeutic measures in DVT include staying as active as possible, use of graduated elastic compression stockings, and medicines for pain relief.

PE requires hospitalisation and is managed as an emergency. Medicines that dissolve the clot (thrombolytics) and prevent the formation of more clots (anticoagulants) are prescribed.

Support measures like ventilator, medicines for the heart, etc, may be necessary in life-threatening PE. Surgery is sometimes needed for patients at great risk for another PE.

At the post-natal visit, the obstetrician will elucidate any family history of thrombosis and discuss investigations, contraceptive options, the management of future pregnancies, and advise on the use of a graduated elastic compression stocking on the affected leg for two years.

Preventing clots

VTE can be prevented by measures that include staying as active as possible, smoking cessation, maintenance of hydration by drinking adequate amounts of fluids, wearing graduated elastic compression stockings, and weight reduction prior to getting pregnant, if overweight.

Pregnant women who have certain risk factors, eg previous DVT, would also be prescribed prophylactic heparin.

Dr Milton Lum is a member of the board of Medical Defence Malaysia. This article is not intended to replace, dictate or define evaluation by a qualified doctor. The views expressed do not represent that of any organisation the writer is associated with. For further information, e-mail starhealth@thestar.com.my. The information provided is for educational and communication purposes only and it should not be construed as personal medical advice. Information published in this article is not intended to replace, supplant or augment a consultation with a health professional regarding the reader’s own medical care. The Star does not give any warranty on accuracy, completeness, functionality, usefulness or other assurances as to the content appearing in this column. The Star disclaims all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.

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