Women with subclinical hypothyroidism and thyroid autoimmunity are thought to have an increased risk of adverse pregnancy outcomes; however, the risk of miscarriage is not well defined. Now, a study of 3,315 women in iodine-sufficient areas of China has assessed the effect of these conditions at 4–8 weeks gestation on subsequent risk of miscarriage. Compared with women with normal thyroid function, women with subclinical hypothyroidism and/or thyroid autoimmunity had an increased risk of miscarriage. The risk was greatest in women who had both conditions. In addition, miscarriages in women with these conditions occurred at an earlier gestational age than miscarriages in women who had normal thyroid function.