TSH test is alone is usually adequate to start medicine if TSH is not within the normal range/ or shows hypothyroidism. In your case, TSH is within the normal range, although higher side of normal for pregnancy. Prior to starting medicine, it’s recommended to check TPO antibodies to determine cause of hypothyroidism, and free T4 and free T3 levels as well to help decide dose. TSH of 2.5 or less is recommended if you have preexiting hypothyroidism on medication or if TPO antibody is positive. The chances of TSH returning to normal after pregnancy depend on cause of hypothyroidism If thyroid medicine is started, thyroid tests should be repeated in 4 weeks

First trimester is the most crucial period and one must not self medicate during this time at least. U must consult an endocrinologist so as to keep your thyroid levels within target range throughout pregnancy. TSH goes up and thyroxin requirement goes up during pregnancy and may come back to prepregnancy levels after delivery