Blood Clot during Pregnancy

by | June 23, 2020

What is a blood clot during pregnancy?

A blockage in a blood vessel is called a blood clot or thrombosis. A blood clot can occur in both the arterial (for blood from the heart) and venous blood vessels (for blood to the heart) in the circulatory system. If this occurs during pregnancy, it is almost always a venous blood clot. The condition has varying degrees of severity, but in the short term can be life-threatening and in the long term can lead to serious complications. The risk of blood clots is probably 10 times higher in a pregnant woman than a non-pregnant woman.

A deep vein thrombosis is a blood clot that sits in the deep veins of the calf or thigh. In exceptional cases, such a blood clot can be dissolved (embolized) and monitor blood flow to the heart and lungs, so-called pulmonary embolism.

Blood Clot during Pregnancy

Deep vein thrombosis occurs in 0.5 to 3.0 of 1,000 pregnancies and is the leading cause of death among pregnant women in the United States. Approximately 50% of all blood clot cases associated with pregnancy occur in the postnatal period. With a previous blood clot, the risk is about 10% in a new pregnancy. 1 per 700 gets deep vein thrombosis during the postpartum period. 1 in 2,500 gets pulmonary embolism during pregnancy. The condition occurs just as often in all trimester and after birth.

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Blood vessel damage, infection and tissue damage in combination with increased blood supply tendency and disturbances of blood flow, initiates processes that result in deep vein thrombosis. During pregnancy, the pregnant uterus presses the blood vessels in the abdomen and leads to decreased blood flow. In addition, hormonal changes lead to blood clotting more easily in pregnant women than in women without pregnancy.

Embolism can occur if parts of a blood clot become detached, follow the blood flow and attach to a smaller blood vessel.

The risk of blood clots during pregnancy increases with age (> 40 years), obesity (BMI> 30), number of previous children, family history of blood clot disease and pregnancy poisoning. Pregnancy itself is a risk factor for developing blood clots. Other factors that increase the risk are smoking, caesarean section, bed position and obesity / obesity. Hereditary disorders of the blood supply system (thrombophilia) significantly increase the risk of blood clots as well as some systemic inflammatory diseases.

What are the symptoms of blood clots?

The symptoms of deep vein thrombosis can range from very vague to severe pain in the calf or thigh. Both when the legs are at rest and during walking, there may be pain. Depending on the place, the calf or thigh may be swollen and hot. Some may also have a fever.

In the case of blood clots in the lung, quite sudden chest pain occurs. Heavy breathing, palpitations and coughing and bloody coughing may occur. With large blood clots you become cold, moist and pale, the pulse becomes weak, blood pressure drops and you eventually faint. Large pulmonary embolism can be life-threatening.

How is the condition diagnosed?

Disease history and typical findings may cause the doctor to suspect that there is a blood clot. However, diagnosis is easy to overlook and only 10% of those suspected of having a blood clot are found to have it.

Ultrasound is the preferred, first method of examination for suspected deep vein thrombosis. The study is safe, has high diagnostic accuracy and is reasonable. A blood test (D-dimer) is also useful in the investigation but pregnancy itself can give an elevated level. If D-dimer is negative and ultrasound is negative, the risk of blood clots is very small. In cases where a blood clot is still suspected, venography may be necessary. Then, contrast fluid is injected into a blood vessel (vein) in the foot. In case of blood clots, the transport of contrast agents is blocked and the diagnosis can be made. In exceptional cases, CT or MRI is done.

A successful way of diagnosing pulmonary embolism is to take D-dimer tests and do bone / thigh ultrasound. If both of these examinations are normal, it strongly opposes pulmonary embolism. With continued uncertainty about the diagnosis, it is recommended to do a so-called spiral CT.


You can do a lot of things yourself to avoid getting a blood clot during pregnancy. It is important to be physically active. The risk of blood clots is probably a good reason to stop smoking during pregnancy (as well as after birth!). You should not lie to bed for any length of time. You may want to use an elastic sock to prevent fluid buildup in the tissues of your legs.

Both blood clots in the legs and lungs are emergency medical conditions that require hospitalization. The treatment there is with blood thinners (heparin / low molecular weight heparin). In the case of life-threatening pulmonary embolism, surgical treatment may be necessary.

In both deep vein thrombosis and pulmonary embolism, treatment with low molecular weight heparin (LMWH) is recommended. However, for the first 24 hours, pulmonary embolism in pregnant women is still treated with intravenous heparin. The low molecular weight heparin is given as an injection just below the skin (subcutaneously). After discharge from the hospital, you continue to administer the syringes yourself. It is recommended that the treatment lasts for 3–6 months during pregnancy, including 6–12 weeks after birth, depending on when the blood clot appeared and where it was placed. After birth, treatment can be changed to warfarin tablets. In women with significant blood clot risk, long-term treatment longer than 1 year is recommended.

In the case of previous blood clots, prophylactic treatment with low molecular weight heparin should be given throughout pregnancy and 6-12 weeks after delivery.


In the case of a previous severe clot disease or in a hereditary or acquired coagulation defect, low molecular weight heparin should be given throughout the pregnancy in subsequent pregnancies. Research has shown that preventive treatment with LMWH is safe and effective during pregnancy. Preventive treatment is usually given 6-12 weeks after birth.


If treatment is not given to pregnant women with deep vein thrombosis, pulmonary embolism will occur in 15–25% of cases. Untreated, the mortality of pulmonary embolism is up to 30%, and 3–8% of patients do not survive pulmonary embolism despite treatment.

Of those treated for pulmonary embolism, two-thirds are completely healthy, while the last third receives some reduced blood flow and disturbed function in the lungs.

30-60% of women who get deep vein thrombosis during pregnancy may later suffer from post-thrombotic disorders. This is characterized by a feeling of weight in the legs (both during walking and at rest), pain, swelling, varicose veins, discoloration of the skin, eczema and leg ulcers. Continuous use of individually tailored elastic stockings reduces the risk of developing such a syndrome afterwards by 50%.