What Are The Side Effects Of Eltroxin 100mcg During Prgnancy?

my wife is pregnant and in 9th week of pregnancy. she had thyroid problem and hence taking electroxine 100mcg. Last year we had checked it was normal but doctor has asked to continue the tablet. Now we have test the thyroid is it advisable to do test during her intial pregnancy. Is it required to continue the tablet.? will it affect the child by any means? suggest me appropriate time to check the risks involved?
Regards
Bala