My Name Is Prashanthi, Am 4th Month Pregnant Before Conceive

My Name is Prashanthi, am 4th month pregnant before conceive I have a hyperthyroid (TSH is 0.1) Then I used neo-carbimazole after conceiving I went to doctor she suggested use propylthiouracil instead of neo-carbimazole am using that twice a day,but now I have TSH level is <0.01, and T4 low,my doctor suugest stop PTU.If T4 is low is it harmful to my baby please suggest