I am sorry no one has answered your question. I don't have percentages for you. But this is my understanding: Most women do not ovulate if their thyroid levels are not normal (this is how thyroid issues causes infertility). Once your levels are with in normal range it would be easier to get pregnant.
Thyroid meds are considered natural substitutes and can be taken safely during pregnancy, even at high doses.
You should look for a high risk OBGYN or better an Endo/OBGYN who understands your condition. You and the baby would have to be monitored closely during your pregnancy and after delivery. But everything I know says that having a baby is possible after a TT. It will just be a little more work to have a health baby.
I hope this helps, but again my best advise would be to find the right doctor and ask all these question and the thousands more that you will think of as you decide to have a baby. Every women and thyroid condition is different. Only a doctor can tell you if and when it is safe for you try to get pregnant and have a baby.
Good luck and I hope you can have a healthy, happy little one.
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