A 32-year-old woman is evaluated for a prepregnancy assessment. She has a heart murmur but is asymptomatic. She has no history of atrial fibrillation. Her only medication is prenatal vitamins.
On physical examination, blood pressure is 102/60 mm Hg and pulse rate is 70/min and regular. The estimated central venous pressure is elevated. The apical impulse is tapping, and there is a parasternal impulse at the left sternal border. The S1 and S2 are loud, and a grade 2/6 diastolic decrescendo murmur is heard at the apex. No opening snap is appreciated. The lungs are clear, and there is no edema.
A transthoracic echocardiogram demonstrates normal left ventricular size and function. The mitral valve is thickened with diastolic doming. The mitral valve mean gradient is 12 mm Hg; the calculated mitral valve area is 0.9 cm2. There is no mitral valve regurgitation. The estimated pulmonary artery systolic pressure is 55 mm Hg.
Which of the following is the most appropriate management at this time?