In the linked systematic review (doi:10.1136/bmj.d2616), Thangaratinam and colleagues assess the association of thyroid autoantibodies with miscarriage and preterm birth in biochemically euthyroid women and the effect of levothyroxine treatment on pregnancy outcomes.1

An association between thyroid antibodies and miscarriage was first reported in 1990.2 The finding was serendipitous—the prospective study was originally designed to evaluate the incidence and causes of postpartum thyroiditis. As the study progressed, the unexpected number of spontaneous miscarriages in euthyroid women with thyroid antibodies prompted the researchers to assess pregnancy outcome in the 552 women who were initially screened in the first trimester. The rate of miscarriage in thyroid antibody positive women was twice that seen in thyroid antibody negative women (17.0% v 8.4%; P=0.01). The increased rate of pregnancy loss was not related to differences in maternal age, cardiolipin antibody status, pregnancy history, or concentration of thyroid stimulating hormone. Similarly, the initial discovery of a significant association between thyroid antibodies and preterm delivery seems to have been by …