A number of controversies continue to fuel debate including: (i) the target range for thyroid stimulating hormone (TSH) in women with subfertility planning pregnancy, (ii) management of mild thyroid hypofunction before and during pregnancy, (iii) the treatment of thyroid peroxidase (TPO) antibody-positive euthyroid women with levothyroxine, (iv) the optimal choice of antithyroid treatment in women with hyperthyroidism. This evidence concerns the gene TPO and hyperthyroidism.