Hello,
Welcome to the ehealthforum and I am glad to help you. It is okay to conceive once the TSH has decreased to < 4.5.
However, we usually tend to keep it on the lower side of normal i.e. between 1 & 2. It is important to know that the dose of L-thyroxine is increased by 50% once the pregnancy sets in.
Please consult an endocrinoogist for the same. I sincerely hope that helps. Take care.