As you are planning for pregnancy your TSH should be below 2.5 uIU/ml. So it is important to start l thyroxine replacement. It is not always true that if you start medicines you have to continue it lifelong. If you require l thyroxine replacement for lifelong then that is a separate issue. As it is sub clinical hypothyroidism there is a chance to drop l thyroxine replacement in future.

Hello, As u are planning pregnancy plan is keep TSH below at least 3 so u need to start the tablet and titrate the doses as per TSH 2 monthly.. Post pregnancy thyroid medication can be tapered and within normal limits we can give trial of stopping the dose as your TSH is very borderline high... So whether to continue or not that will be decided later on