Thank you for your query at DoctorSpring.com
I understand your concern.
TSH of 0.042mIU/l on Thyronorm 125mcg is satisfactory for a patient who has had surgery for thyroid cancer. This ensures that whatever thyroid cells are remaining will remain suppressed.
Pregnancy if positive during this stage is OK. Thyroid reports like this will not harm the baby. During pregnancy, a little suppressed TSH is better than an elevated TSH. So don't worry.
Feel free to discuss further,