Dear Practo user, Serum TSH levels are rather high. Has it been done earlier during non pregnant state? If it was normal earlier, get it repeated. Treatment for this should start immediately. Yes, it may have effect on mental development. However, the incidence is not high. But, one cannot give guarantee that the child will be completely normal. Even when all the investigations are normal, there is a small chance of child having abnormality. As such, there is no indication of terminating pregnancy. You have to take the call on that. If the treatment is started immediately, chances of it being abnormal are less.