This is designed as a phase IV study on treatment with a cohort size of pregnant women and women in whom embryo transfer is expected within 60 days with TSH value into the normal range (0.4-2.5 mUI/mL) and Tgab and/or TPOab positivity. We have performed two randomizations arms: Randomization arm A will include women LT4 replacement-free that will take Selenium or Placebo and Randomization arm B will include women already under LT4 replacement that will take Selenium or Placebo. Patients included in Randomization A will move into Randomization B, if TSH increases above 2.5 mUI/mL during pregnancy.