A 23 year old asymptomatic woman attends her family physician for thyroid function testing as her mother has recently been commenced on levothyroxine. Thyroid functiontests (TFTs) show TSH 6miU/L, and free T4 of 12.4 pmoi/L (0.96 ng/dL). Her serum thyroid peroxidase antibodies are strongly positive. What is the most appropriate management plan?