Final answer:
Heparin is the medication used to treat deep vein thrombosis (DVT) in pregnant patients due to its safety profile, as it does not cross the placental barrier.
Step-by-step explanation:
The medication used to treat deep vein thrombosis (DVT) in pregnant patients is heparin. Unlike warfarin, heparin does not cross the placental barrier and thus is safer for both the mother and the developing fetus. Warfarin, on the other hand, is contraindicated in pregnancy due to the risk of fetal malformations. Medications such as rivaroxaban, dabigatran, and apixaban are also not recommended during pregnancy. Heparin can be administered as unfractionated heparin or as low molecular weight heparin, with the latter often being preferred due to its better safety profile and more predictable response.