A 29-Year-Old Woman, Gravida 1 Para 0, at 28 Weeks

A 29-year-old woman, gravida 1 para 0, at 28 weeks gestation comes to the office to establish prenatal care after recently moving to a new city. She has had no complications in this pregnancy and had a normal anatomy ultrasound at 20 weeks gestation. On physical examination, the fundal height measures 28 cm. Cardiac auscultation reveals a 2/6 blowing systolic murmur best heard at the left sternal border. The murmur intensifies with inspiration, and there is no ejection click or palpable thrill at the sternal notch. The lungs are clear to auscultation. There is 1+ pitting edema to the midshins bilaterally. Which of the following is most likely responsible for this patient's murmur?

A) Bacterial vegetations on the mitral valve
B) Calcification of a bicuspid aortic valve
C) High blood flow across the pulmonic valve
D) Inflammatory stiffening of the tricuspid valve
E) Myxomatous degeneration of the mitral valve