**Core Concept**
During pregnancy, the risk of thromboembolic events increases due to the hypercoagulable state caused by increased levels of coagulation factors and venous stasis. Women with a history of thromboembolic disease require careful management to prevent recurrence.

**Why the Correct Answer is Right**
This patient has a history of deep vein thrombosis (DVT) and pulmonary embolism (PE) during her first pregnancy, which was treated with heparin and warfarin. She is now pregnant again and is at increased risk for recurrent thromboembolic events. The American College of Chest Physicians (ACCP) recommends the use of low-molecular-weight heparin (LMWH) or unfractionated heparin for the prevention of recurrent thromboembolism in pregnant women with a history of DVT or PE. This is because warfarin is teratogenic and crosses the placenta, increasing the risk of fetal bleeding and other complications.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because aspirin is not sufficient for the prevention of recurrent thromboembolism in pregnant women with a history of DVT or PE. While aspirin may be used as an adjunctive therapy, it is not a substitute for anticoagulation.
**Option B:** This option is incorrect because warfarin is contraindicated in pregnancy due to its teratogenic effects and risk of fetal bleeding.
**Option C:** This option is incorrect because the use of warfarin in pregnancy would not be appropriate for this patient, given her history of thromboembolic disease.

**Clinical Pearl / High-Yield Fact**
Pregnant women with a history of thromboembolic disease require careful anticoagulation management to prevent recurrence. Low-molecular-weight heparin (LMWH) or unfractionated heparin are recommended for the prevention of recurrent thromboembolism in these patients.

**Correct Answer: D.**