Pregnancy Complicated by Venous Thrombosis

A 37-year-old primigravid woman presents at 12 weeks of gestation with a painful, swollen left leg, breathlessness, and lower abdominal pain. She has had hyperemesis for several weeks. She has no personal history of venous thrombosis, but she reports a family history of thrombosis in both her mother and her maternal aunt. On examination, she has a body-mass index (BMI, the weight in kilograms divided by the square of the height in meters) of 36, and the entire leg is dusky and swollen. No abnormalities are detected on pulmonary examination, and the oxygen saturation is normal. How should her case be evaluated and treated?