Venous thromboembolism in pregnancy: Clinical sciences

Venous thromboembolism, or VTE for short, is when clots form within the venous system, leading to complications that include deep vein thrombosis, or DVT, and pulmonary embolism, or PE. While patients are at increased risk for VTE as early as the first trimester, their highest risk occurs in the first 1 to 2 weeks postpartum.

If your patient presents with a chief concern suggesting venous thromboembolism in pregnancy, you should first perform an ABCDE assessment to determine if they are stable or unstable. If unstable, stabilize their airway, breathing, and circulation. Next, obtain IV access and place your patient on continuous vital sign monitoring, including blood pressure, heart rate, and oxygen saturation. Don’t forget that you have two patients, so be sure to assess fetal heart rate, and depending on gestational age, consider continuous fetal monitoring as well. Finally, if needed, provide supplemental oxygen.

Okay, let’s go back to the ABCDE assessment and talk about stable patients. In this case, start by obtaining a focused history and physical examination. During pregnancy, most cases of VTE are caused by DVT, and unlike non-pregnant patients, the thrombus tends to be more proximal, typically in the iliac vein and iliofemoral veins, and occurs more frequently in the left lower extremity compared to the right. These patients will usually present with unilateral extremity pain and swelling.

History might also reveal some risk factors for DVT, with the most important one being a personal history of thrombosis. Others include having a C-section; obesity; hypertension, preeclampsia, or eclampsia; and having an acquired or inherited thrombophilia.

The most reliable physical exam finding is a difference in calf circumference measurements of at least 2 centimeters. You might also be able to palpate the thrombotic vein, which could be erythematous, warm, and tender. Labs are typically not necessary for diagnosis.

Time for a clinical pearl! While serum D-dimer assays are useful to rule out DVT in non-pregnant patients, this test is not reliable during pregnancy and postpartum, as physiologic levels are normally elevated.

Now, if your patient has these history and exam findings, obtain a lower extremity compression ultrasound. If it shows poor compressibility of a proximal lower extremity vein, your diagnosis is DVT. Treatment begins with therapeutic anticoagulation with low molecular weight heparin, such as enoxaparin.

If your patient never had thrombophilia testing, consider the best time interval for it. While some molecular genetic tests can be performed at any time, other non-molecular tests, such as for Protein C and Protein S deficiencies, should be done at least 3 months postpartum. Ideally, the best timing for thrombophilia testing is when your patient is not pregnant or lactating, is not taking anticoagulation, and is not taking hormonal contraception.

If maternal and fetal status are reassuring, plan for vaginal delivery at 39 weeks unless otherwise contraindicated. Once your patient has delivered, resume anticoagulation if it was on hold. Typically you’ll want to continue anticoagulation for at least 3 months, which includes the 6 week postpartum window. The actual duration of anticoagulation varies depending on your patient’s history. For those who require anticoagulation for more than 6 weeks postpartum, consider transitioning to oral therapy with warfarin.

Here are a couple of high-yield facts! Warfarin, a vitamin K antagonist, is often used for long-term anticoagulation outside of pregnancy. It’s rarely used during pregnancy, except in those with a high thrombotic risk, such as having a mechanical heart valve. That’s because it can cause warfarin embryopathy in the first trimester and may cause significant fetal hemorrhage later in pregnancy if delivery occurs unexpectedly.

So, if your patient requires warfarin, it should be replaced with unfractionated heparin in the first trimester and around the time of delivery. On the flip side, warfarin is compatible with breastfeeding, since it doesn’t accumulate in breast milk and doesn’t cause an anticoagulation effect on the newborn. Therefore, lactating patients who require long-term anticoagulation can be transitioned to warfarin postpartum.