Thyroid TSH level during 3rd trimester

Hi moms.. Got my thyroid results for 3rd trimester and tsh value is 3.38 and expected pregnant women tsh should be less than 3.0 mlU/L. Doctor suggested me to take 25mcg thyroxine tablets. What im thinking is if I take these tablets now.. should I continue thyroid tablets lifelong with low doses ??? Pls suggest me coz already my sister also got thyroid during her pregnancy and now she's taking tablets for thyroid regularly.