Autoimmune thyroid diseases, including Graves disease and autoimmune thyroiditis, are common in women of childbearing age. Poorly controlled Graves disease is associated with an increased risk of fetal loss, premature birth, pre-eclampsia, intra-uterine growth retardation, and thyroid storm. Antithyroid drugs, propylthiouracil and carbimazole (or its metabolite methimazole), cross placenta and may cause hypothyroidism and goitre in the fetus. Carbimazole is associated with characteristic embryopathy, whilst propylthiouracil has also been shown to be associated with liver failure and congenital malformations. Women presenting with Graves disease before and during pregnancy must be counselled about the risks of uncontrolled thyrotoxicosis and adverse effects of antithyroid drugs. Autoimmune thyroiditis can manifest as overt or subclinical hypothyroidism. Both overt and subclinical hypothyroidism in pregnancy is associated with impaired neurological development of the offspring and other adverse pregnancy outcomes, including miscarriage, premature birth, pre-eclampsia, low birth weight and gestational diabetes. Women with hypothyroidism need increased dose of levothyroxine in pregnancy to remain euthyroid. Recent studies have highlighted suboptimal management of hypothyroidism in pregnancy, with associated adverse pregnancy outcomes. Whether all pregnant women should be screened for thyroid function remains controversial. About one in ten euthyroid women have thyroid peroxidase or thyroglobulin antibodies. These women carry an increased risk of subfertility, miscarriage, and premature birth. One randomised controlled trial has shown that levothyroxine in such women may reduce the risk of miscarriage and premature birth. This presentation will discuss impact of autoimmune thyroid diseases in pregnancy, and evidence base for their management.