From the Guidelines
Yes, pregnancy itself increases the risk of thrombosis, regardless of previous birth control use or history of deep vein thrombosis (DVT). During pregnancy, a woman's blood naturally becomes more likely to clot (hypercoagulable) to prevent excessive bleeding during delivery. This hypercoagulable state, combined with compression of pelvic veins by the enlarging uterus and decreased mobility, creates a 5-10 fold higher risk of venous thromboembolism compared to non-pregnant women. The risk is highest in the third trimester and immediate postpartum period. Women with a previous history of DVT, including those who experienced it while on birth control during long flights, should inform their obstetrician about this history early in pregnancy. They may require prophylactic anticoagulation therapy (typically low molecular weight heparin like enoxaparin) during pregnancy and for 6 weeks postpartum, as suggested by the American College of Chest Physicians evidence-based clinical practice guidelines 1. The dosage and timing would be determined by their healthcare provider based on individual risk factors, with guidelines recommending antepartum prophylaxis with prophylactic- or intermediate-dose LMWH for pregnant women at moderate to high risk of recurrent VTE 1. Regular movement, proper hydration, and compression stockings may also be recommended as preventive measures during pregnancy.
Some key points to consider include:
- The hypercoagulable state of pregnancy increases the risk of thrombosis, regardless of previous birth control use or history of DVT
- Women with a previous history of DVT should inform their obstetrician about this history early in pregnancy
- Prophylactic anticoagulation therapy may be required during pregnancy and for 6 weeks postpartum
- The American College of Chest Physicians recommends antepartum prophylaxis with prophylactic- or intermediate-dose LMWH for pregnant women at moderate to high risk of recurrent VTE 1
- Regular movement, proper hydration, and compression stockings may also be recommended as preventive measures during pregnancy.
In terms of management, prophylactic anticoagulation therapy with low molecular weight heparin is recommended for pregnant women at moderate to high risk of recurrent VTE 1. This should be determined by their healthcare provider based on individual risk factors. The guidelines also recommend that women receiving anticoagulation for the treatment of VTE who become pregnant should be treated with LMWH over vitamin K antagonists during the first trimester, second and third trimesters, and during late pregnancy when delivery is imminent 1.
From the Research
Risk of Thrombosis During Pregnancy
The risk of thrombosis is elevated during pregnancy due to various factors, including:
- Hypercoagulability, which is present as early as the first trimester 2
- Genetic and acquired risk factors, such as thrombophilia and a history of thrombosis 3, 4
- Physiological changes during pregnancy, including slowing of blood flow and increase in circulating blood volume 5
Factors that Increase the Risk of Thrombosis
The following factors increase the risk of thrombosis during pregnancy:
- History of thrombosis, with a 3.5-fold increased risk of recurrent VTE during pregnancy compared to non-pregnant periods 6
- Thrombophilia, including inherited and acquired thrombophilia 2, 3
- Certain medical conditions and complications of pregnancy and childbirth 2, 4
- Previous venous thrombosis, with a relative risk of pregnancy-associated VTE between 3.4 and 15.2 6
Management of Thrombosis During Pregnancy
The management of thrombosis during pregnancy includes:
- Anticoagulation therapy, with heparins being the preferred agents due to their ability to not cross the placenta 6, 2, 3
- Prophylactic anticoagulation for women with a history of thrombosis, thrombophilia, or other risk factors 6, 3
- Continued anticoagulation therapy for at least 6 weeks after delivery due to the higher risk of thrombosis postpartum 3