**3.5 Malignant conditions**

Primary thromboprophylaxis of ambulatory cancer patients should be decided according to the individual risk of bleeding, the type of cancer, or the stage of the disease [37]. For hospitalized patients without acute venous thromboembolism or a history of venous thromboembolism, the American Society of Hematology recommends thromboprophylaxis with low molecular weight heparin, but only for the duration of the hospital stay. If during hospitalization a patient has undergone surgery or if a patient is receiving outpatient systemic chemotherapy and is at high risk of thrombosis, continued administration of LMWH has been shown to be beneficial. Oral anticoagulation, in the form of vitamin K antagonists or DOAC, is not included in current guidelines because there is insufficient data on its efficacy [38].

For a patient with active cancer who develops venous thromboembolism, initial treatment can be with either LMWH or DOAC, the latter being the medication of choice. It is recommended to continue treatment for at least 3–6 months, which may be extended as a secondary prophylactic measure in patients with active cancer and/or recurrence of venous thromboembolism. Direct oral anticoagulation remains the first choice of treatment in this case as well [38].

In a cancer patient with visceral or splanchnic venous thrombosis, according to the guidelines, treatment should consist of short-term anticoagulation (3–6 months) or clinical observation [38].

#### **3.6 Pregnancy**

Despite the prothrombotic status of physiological changes occurring during pregnancy, prophylactic anticoagulation of asymptomatic patients with no history of venous thromboembolism should be judged on a case-by-case basis [21, 39].

Anticoagulation for a venous thromboembolism event should be with LMWH if occurring before the 36th week of pregnancy and should be switched to unfractionated heparin afterward to minimize complications of epidural anesthesia. Vitamin K antagonists are not recommended after the first trimester as they are known to cause "warfarin embryopathy." Direct oral anticoagulation is also not approved for administration during pregnancy [21, 40].

Following an episode of venous thromboembolism, anticoagulation should be continued for 3–6 months, or 4–6 weeks postpartum, with either low molecular dose heparin or unfractionated heparin [21].

Patients with antiphospholipid syndrome and a history of thrombotic complications during previous pregnancies may benefit from prophylactic anticoagulation during pregnancy and for an additional 6 weeks postpartum [34].

#### **3.7 SARS-CoV-2**

Anticoagulation management of patients with Covid-19 depends on the severity of the disease. The administration of unfractionated heparin to patients hospitalized in an uncritical state has been observed to reduce the need for intensive care maneuvers, such as specific organ support or intubation, and also reduces the death rate. On the other hand, the condition of critically ill patients has not been improved by heparin treatment, and heparin treatment actually increases the rate of complications and is subsequently not recommended [41].

After discharge, patients with high thrombotic risk and a low bleeding risk could benefit from low-dose rivaroxaban treatment for an optimal duration to be determined [41].
