Hello. welcome to HCM.
yes, a hypothyroid state if left untreated effects the baby. It is best to be euthyroid before getting pregnant and by maintaining it throughout pregnancy
. In addition it is important to check the baby for thyroid as soon as possible after birth, which is a standard practice in most hospitals these days. Effective weight reduction will follow the same norms as for a non-hypothyroid person. eat healthy and exercise regularly. You have to take advice of your endocrinologist
doctor both, if you want to continue both medicines in parallel.