DVT and Pregnancy

Although the absolute incidence of venous thromboembolism in pregnancy is low (1 or 2 cases per 1000 pregnancies), this risk is approximately five times as high as the risk among women who are not pregnant. These risks reflect the venous stasis and procoagulant changes in coagulation and fibrinolysis, which are considered to be part of physiologic preparation for the hemostatic challenge of delivery.

The clinical diagnosis of venous thrombosis is unreliable in pregnancy. Suggestive symptoms and signs, such as leg swelling and dyspnea, may be difficult to differentiate from the physiologic changes of pregnancy. As compared with deep-vein thrombosis in nonpregnant persons, deep-vein thrombosis in pregnant women occurs more frequently in the left leg (85%, vs. 55% in the left leg among nonpregnant persons) and is more often proximal (72% in the iliofemoral veins, vs. 9% in the iliofemoral veins among nonpregnant persons), with a greater risk of embolic complications and the post-thrombotic syndrome. Thrombotic events occur throughout pregnancy, with more than half occurring before 20 weeks of gestation. The risk increases further in the puerperium (the 6-week period after delivery), probably owing to endothelial damage to the pelvic vessels that occurs during delivery. Recent data indicate that an increased relative risk (but low absolute risk) persists until 12 weeks after delivery. However, approximately 80% of postpartum thromboembolic events occur in the first 3 weeks after delivery.

Suspected deep-vein thrombosis is best assessed by means of compression duplex ultrasonographic examination, including examination of the iliofemoral region. In women with a negative result on ultrasonography in whom clinical suspicion of deep-vein thrombosis is high, it may be prudent to repeat the test after 3 to 7 days. In cases in which iliocaval venous thrombosis is suspected but ultrasonography cannot detect a thrombus, magnetic resonance or conventional x-ray venography may be considered. Chest radiographic findings are normal in the majority of cases of pulmonary embolism, but they can show pulmonary features that point to an alternative diagnosis or nonspecific features of pulmonary embolism such as atelectasis or regional oligemia. Since deep-vein thrombosis is often present in patients with pulmonary embolism, ultrasonographic venography is useful in patients who have possible symptoms or signs of deep-vein thrombosis. If deep-vein thrombosis is detected, further radiologic studies do not have to be performed to confirm a pulmonary embolism. In women with normal findings on chest radiography, ventilation–perfusion lung scanning is often recommended, since it has a high negative predictive value, owing to the low prevalence of coexisting pulmonary problems that can result in indeterminate or false positive results. Moreover, the ventilation component can often be omitted, thereby minimizing the dose of radiation to the fetus. Whereas computed tomographic (CT) pulmonary angiography (CTPA), with its high sensitivity and specificity, is usually the first-line test to detect pulmonary embolism in nonpregnant patients, it is used less often in pregnant women.

One diagnostic study frequently used is the D-dimer. Pregnancy is a hyper coagulable state and therefore, D-dimer need to be adjusted. There is growing evidence that trimester adjusted D-dimer is safe, reduces testing without missing more clots. 1st trimester cut off can be 50% more than the normal laboratory value, during the 2nd trimester 100% and 3rd trimester 150% the normal value. Of note, D-dimers normalize to the pre-pregnancy value after 4-6 weeks.

Anticoagulation in pregnancy typically involves unfractionated heparin or low-molecular-weight heparin, which do not cross the placenta or enter breast milk. In contrast, vitamin K antagonists such as warfarin are contraindicated in pregnancy, since they cross the placenta and their use is associated with embryopathy, central nervous system abnormalities, pregnancy loss, and fetal anticoagulation with possible bleeding. Low-molecular-weight heparins have largely replaced unfractionated heparin for the management of venous thromboembolism in pregnancy. Typical agents include dalteparin (at a dose of 200 IU per kilogram of body weight daily or 100 IU per kilogram twice daily), enoxaparin (1.5 mg per kilogram daily or 1 mg per kilogram twice daily), and tinzaparin (175 units per kilogram daily). Data are limited regarding the use of fondaparinux in pregnancy. Oral direct thrombin inhibitors such as dabigatran and anti–factor Xa inhibitors such as rivaroxaban should generally be avoided during pregnancy. These agents may cross the placenta with possible adverse fetal effects. Thrombolysis in pregnancy is reserved for massive life-threatening pulmonary embolism with hemodynamic compromise or for proximal deep-vein thrombosis that is threatening leg viability. Caval filters are sometimes used in women who have recurrent pulmonary embolisms despite adequate anticoagulation or in whom anticoagulation is contraindicated, or in women in whom acute deep-vein thrombosis has developed close to the time of delivery.

Women should be advised to discontinue injections of heparin if labor starts or is suspected. Neuraxial anesthesia is usually deferred until at least 24 hours after the last dose, given a small risk of epidural hematoma associated with administration of neuraxial anesthesia before that time. After delivery, low-molecular-weight heparin should not be administered for at least 4 hours after spinal anesthesia or removal of an epidural catheter. After delivery, anticoagulant treatment is continued for at least 6 weeks, with a minimum total duration of 3 months.