What is deep vein thrombosis?

Deep vein thrombosisis the development of a blood clot in a deep vein. During pregnancy, up to 90 percent of DVTs occur in the left leg. Early treatment can keep a clot from breaking off and traveling through the circulatory system to the lungs (called a pulmonary embolism), which can be life-threatening.

During pregnancy, the risk of venous thromboembolism (VTE) is increased at least five times compared with non-pregnant women of the same age, while the relative risk in the postpartum period can be as high as sixty times. Pregnancy and the puerperium are well-established risk factors for venous thromboembolism, and there is also long term morbidity associated with the postthrombotic syndrome (PTS).

The majority of women, who suffer from DVT during pregnancy, develop sequelae that range from edema and skin changes to recurrent thrombosis and ulceration. Certain conditions have been associated with the highest risk of pregnancy related DVT. These include inherited or acquired thrombophilias, a previous history of thrombosis, antiphospholipid syndrome, lupus, heart disease and sickle cell disease . When these are present, the need for prophylactic anticoagulation should be addressed .

Other independent risk factors are age 35 and older, null parity, multiple gestations, obesity and immobility, these increase the risk 1.5–2 fold . In the puerperium, post-partum infection increases the risk of thrombosis by 4-fold and cesarean delivery increases the risk 2-fold.  

How common is deep vein thrombosis?

Venous thromboembolism, which includes both deep vein thrombosis and pulmonary embolism, occurs in about two in every 1,000 pregnancies.

While those numbers make it a relatively uncommon complication, VTE actually crops up about four to five times more frequently in expecting women than in other women of the same age — and 20 times more frequently in the six weeks after birth. By eight weeks postpartum, your risk should drop back to normal.

Signs of DVT during pregnancy and postpartum

The most common symptoms of deep vein thrombosis during pregnancy and postpartum usually occur in just one leg and include: A heavy or painful feeling in the leg (a lot of people say that it feels like a really bad pulled muscle that doesn’t go away), tenderness, warmth and/or redness in the calf or thigh or slight to severe swelling. If the blood clot has moved to the lungs and you have PE, you may experience severe breathlessness , palpitation or sudden loss of consciousness .

Why is DVT more common in pregnancy and postpartum? Who is at risk, mostly?

DVT may be more common during pregnancy because nature, wisely wanting to limit bleeding at childbirth, tends to increase the blood’s clotting ability around birth — occasionally too much.

Experts do know that during pregnancy, the level of blood-clotting proteins increases, while anti-clotting protein levels get lower. Other factors that can contribute to DVT during pregnancy may include an enlarged uterus, which increases pressure on the veins that return the blood to the heart from the lower body, as well as lack of movement due to bed rest.

The risk of thrombosis during pregnancy is attributed to physiological homeostatic changes. During normal pregnancy, the concentrations of the clotting factors fibrinogen, VII, VIII, von Willebrand factor, IX, X, and XII are all increased, resulting in a hyper-coagulation state, which exposes pregnant women to an increased risk of thrombosis.  This mechanism of a hyper-coagulation state of pregnancy is meant to protect women from excessive bleeding during miscarriage and delivery. In developing nations, antepartum hemorrhage is the leading cause of maternal death.  Paradoxically, failed safe mechanism is one of the major causes of maternal death and mortality in western countries.

Moreover, venous stasis that results from a hormonally induced decrease in venous tone and obstruction of venous flow by the enlarging uterus further increases the incidence of VTE in pregnant women. A reduction of venous flow velocity of50% occurs in the legs by weeks 25 to 29 of gestation. This lasts until approximately 6 weeks postpartum, at which time normal venous velocities return. 

Women with a history of VTE have a 3 to 4 times a higher risk of a recurrent VTE during a subsequent pregnancy compared with their risk in their non-pregnant periods.  Approximately 30% of isolated episodes of PE are associated with asymptomatic DVT and in patients presenting with symptoms of DVT,Just like most outcomes of pregnancy age plays an important role is in which women who are over the age of 35 are at higher risk of developing a VTE. Other independent factors include nulliparity, multiple gestations, obesity, and immobility; these increase the risk by 1.5 to 2-fold. 

DVT is more common if you:

l  Have a family or personal history of VTE. 

l  Having thrombophilia (an inherited blood clotting disorder).

l  Are overweight or obese.

l  Smoke.

l  Are on bed rest.

l  Have preeclampsia  or certain chronic illnesses including hypertension, diabetes, inflammatory bowel disease or other vascular diseases.

l  Delivered by cesarean section.

l  Have a postpartum hemorrhage or need a blood transfusion.

How to  prevent DVT?

Be sure to let your doctor know if you have a clotting disorder or if blood clots run in your family. You should also be aware of the signs of a blood clot, since early treatment can reduce the risks of complications like PE.

You can help prevent clots and DVT by keeping your blood flowing in the following ways:

l   Doing plenty of pregnancy safe exercise (as long as you have the okay from your practitioner).

l  Walking if you've been sitting for more than two to three hours.

l  Moving your legs while you’re sitting (raise and lower your heels and then your toes).

l  Taking extra precautions when you travel, including drinking lots of water, getting up frequently to walk (or stretching your legs from a seated position).

If you're at high risk, your practitioner may also prescribe a preventative dose of the blood thinner heparin (or low molecular weight heparin), sometimes during the whole pregnancy or just for several weeks after birth. (Both types of medication do not cross the placenta, so they're safe to take during pregnancy.)

Despite the increased risk for thrombosis during pregnancy and the postpartum period, most women do not require anticoagulation. In most cases the risks of anticoagulation outweigh its benefits.  The mainstay of treatment for pulmonary thromboembolism in pregnancy is anticoagulation with low molecular weight heparin for a minimum of 3 months in total duration and until at least 6 weeks postnatal. Low molecular weight heparin is safe, effective and has a low associated bleeding risk,however determining which patients should receive thromboprophylaxis has always been a challenge. Its rational administration depends on identifying those women who have an increased risk of thrombosis and accurately quantifying this risk. The threshold for recommending post-partum prophylaxis is lower than for antepartum prophylaxis

All women must be provided with the opportunity to participate in shared decision making regarding their management. To make the best decisions, absolute risks and benefits of interventions, guideline recommendations and the patients’ values and preferences must all be taken into account.

Does DVT during pregnancy have any effects on you and your baby?

DVT is a type of venous thromboembolism (VTE), a term for a blood clot in any vein. VTE has been linked to preeclampsia . Many people with preeclampsia have healthy pregnancies and deliver healthy, thriving babies. Left untreated, however, preeclampsia may lead to pregnancy complications.  About 15 to 20 percent of all cases of DVT are linked to antiphospholipid syndrome (APS), an autoimmune disorder that increases the risk of developing blood clots. A tendency to have blood clots, in turn, is known as thrombophilia. APS has been linked to increased risk of recurrent miscarriage, blood clots in the placenta, placental insufficiency (when the placenta is less efficient at getting food and oxygen to the baby), IUGR, and heart attack and stroke in the mother.

Let your doctor know if you’ve had blood clots in the past or recurrent miscarriages; your practitioner may want to run blood tests to check for APS.

Pregnancy-associated VTE remains a leading cause of direct maternal mortality. VTE is approximately 10-times more common in the pregnant population (compared with non-pregnant women) with an incidence of 1 in 1000 and the highest risk in the postnatal period.

Diagnosis of DVT in the pregnant woman

The most common presenting symptoms of DVT are swelling in 88% of pregnant women and 79% of postpartum women and extremity discomfort in 79% of pregnant women and 95% of postpartum women. Additional symptoms include difficulty walking in 21% of pregnant and 32% of postpartum women. Erythema was reported in 26% of both groups. The incidence of isolated DVT in the iliac veins is higher during pregnancy. Isolated iliac vein thrombosis may present with abdominal pain, back pain and/or swelling of the entire leg. These symptoms may be masked by the swelling and discomfort that accompany normal pregnancies, making the diagnosis of DVT during pregnancy more challenging.

Stasis and swelling of the legs can occur due to mechanical compression of the lymphatic vessels and veins which happens with the enlarging uterus. Therefore, edema is a less reliable sign of DVT in pregnant women. Pelvic and back pain may be misinterpreted as normal/expected discomfort or due to musculoskeletal issues, when these symptoms may be emanating from a proximal (ilio-femoral) DVT. These non-specific symptoms are often ignored until the thrombus extends distally into the femoral veins causing pain and swelling of the whole affected leg.

The D-dimer essay is positive even during uncomplicated pregnancies. This indicates increased thrombin activity and increased fibrinolysis following fibrin formation throughout pregnancy, the result of the pregnancy related hypercoagulable state. Thus, this test is non-specific and not reliable for the diagnosis of DVT during pregnancy.

All pregnant women with signs and symptoms suggestive of DVT should have objective testing performed expeditiously, as sudden death is not uncommon among pregnant patients with features compatible with VTE .Unless contraindicated, anticoagulation treatment is recommended when the clinical suspicion is high, until the diagnosis of DVT is ruled out.To confirm the diagnosis in this subset of patients, the use of non-invasive and non-ionizing imaging is preferable. Both, for the health of the fetus as well as the mother as ovaries are radiation sensitive. Currently, there are two such non-invasive methods, ultrasound and magnetic resonance imaging (MRI). Contrast enhanced computed tomography (CT) may be used to diagnose pelvic DVT when MRI is not available, but is not ideal, and not routinely recommended, as it is associated with fetal and maternal radiation exposure.

Routine ultrasonography for the diagnosis of DVT includes direct examination of the thrombus with gray scale imaging, compression technique and color flow Doppler. DVT is diagnosed when the veins fail to compress completely. Sometimes grey scale imaging can demonstrate the thrombus, but this may be limited by a large body habitus or by artefactual intraluminal echoes, thus this is not the primary focus for diagnosis. In obese or very edematous patients, grey scale imaging is limited and the use of color Doppler is helpful to adequately localize the vessels. Compression of the calf or plantar flexion can accentuate the veins, and further assist with adequate imaging.

Compression ultrasonography has a sensitivity of 97% and a specificity of 94% for the diagnosis of symptomatic femoro-popliteal DVT in the general population.Ultrasonography is without risk, inexpensive and readily available. It is the test of choice for pregnant patients with suspected DVT. However, it is less accurate for pelvic vein thrombosis, primarily because of their deep location. Furthermore, the size of the pregnant uterus in the latter half of pregnancy makes imaging of these veins even more difficult. In addition, the compression technique is obviously difficult to perform in the pelvis and much more so in the pregnant pelvis.

Ultrasound should continue to be the primary method of diagnosis of DVT, but if the ultrasound is negative and clinical suspicion is still present, one should not hesitate to order an MRI. MRI is also useful in cases where determining the true extent of a DVT into the pelvis/abdomen will influence management

When to see your doctor?

If you or someone in your close family, such as a parent or sibling, has been diagnosed with DVT, let your practitioner know. Your doctor may run a blood test to see if you have a thrombophilia, which increases your risk of blood clots. If you have thrombophilia, your doctor may want to start you on blood thinners just to be on the safe side.

In addition, if you notice any of the above symptoms (especially during pregnancy or within the first eight weeks after birth), call your practitioner immediately. Your doctor may give you a test (including a blood test, ultrasound or other imaging test) to diagnose a DVT or PE.

If it turns out that you do have a clot, your practitioner will likely treat you with the blood-thinning medication heparin to decrease the blood's clotting ability and prevent further clotting (though your doctor will make other arrangements when labor begins so the heparin doesn't make you bleed excessively during childbirth). Your doctor will also monitor your blood clotting ability along the way.

Pregnancy-related VTE had a significant adverse impact on physical, mental and professional life of women. It also had negative effects on future pregnancy plans.