N2L - I was diagnosed between preg 1 and 2.
First my levels were high, then low. I started 50mg once a day of thyroxine just after I found out I was preg 3rd time, around 5 weeks.
I'm not 100% if this made the difference but the first two pregs were blighted ovums. As far as it had been explained to me, the body needs the hormones to be regulated through the thyroid and piturity gland for baby to develop.
At last check my TSH levels were perfect for pregnancy (11weeks) they were around 2.
That's with the meds.
I'm not sure about mixing with the IVF meds, but if its high avoid iodine. If its low, more more than 250mcg of iodine a day (usually this amount in preg vitamins, not elevit)
So far no side effects from the meds!