Autoimmune thyroid disease with positive thyroid antibodies is a common finding in any population. There is a well recognised link between thyroid autoimmunity, infertility and miscarriage risk. Hypothyroidism which is an underactive thyroid is associated with clear adverse outcomes such as an increase in the rate of placental abruption, premature birth, foetal death and foetal respiratory distress. There may be difficulty interpreting the thyroid function tests due to natural hormone fluctuations at different stages of pregnancy. Despite these difficulties in interpreting the results of blood tests, the thyroxine dose requirements do seem to increase during pregnancy. The key is to monitor regularly and try to obtain gold standard TSH values at each stage of pregnancy.