Question

An otherwise healthy $24$-year-old nulliparous woman comes to the obstetric clinic at $29$ weeks gestation for a scheduled prenatal visit. She reports a recent onset of generalized fatigue and states she frequently needs to catch her breath after walking up a single flight of stairs to her apartment. The patient also notes intermittent "fluttering" sensations in her chest that last for a few seconds and resolve spontaneously. She denies any chest pain, fainting episodes, nighttime coughing, or orthopnea. Routine $28$-week laboratory tests, including a complete blood count and a $1$-hour oral glucose challenge test, performed last week were within normal limits. Her temperature is $37.0^\circ\text{C}$ ($98.6^\circ\text{F}$), blood pressure is $102/62$ mm Hg, pulse is $96$/min, and respirations are $18$/min. On physical examination, the apical impulse is palpated in the fourth intercostal space, slightly lateral to the midclavicular line. Auscultation of the heart reveals a grade $2/6$ systolic ejection murmur at the left upper sternal border and a distinct third heart sound ($S_3$). The lungs are clear to auscultation bilaterally. Trace bilateral pitting pedal edema is noted. An in-office electrocardiogram demonstrates normal sinus rhythm with a leftward shift of the QRS axis compared to her first-trimester baseline, with no ST-segment or T-wave abnormalities. Which of the following is the most appropriate next step in the management of this patient?