Thyroid diseases are very common in women of reproductive age. The aim of this study was to review the current evidence on physiology, pathophysiology, diagnosis and management of women with thyroid disorders that are currently seeking fertility, undergoing assisted reproduction technologies (ART) or being pregnant. Normal thyroid function is essential for normal function of the gonadal axis, thus important in maintaining normal reproductive capacity. On the contrary, any type of thyroid dysfunction may reduce the likelihood of pregnancy; the latter can be restored to normal after appropriate treatment. Over eight million children have been born as a result of assisted reproduction techniques (ART) since 1978. As these procedures are becoming more common in clinical practice, the exact impact of thyroid status on reproductive outcomes as well as that of drugs used in ART on thyroid function has to be fully elucidated. Maternal thyroid function is crucial, especially during the first weeks of gestation, for offspring's wellness and brain development. On the other hand, normal physiological mechanisms during gestation can have a major impact on maternal thyroid function. As human chorionic gonadotropin (hCG) has a thyroid stimulating hormone (TSH)-like effect, high hCG concentrations are associated with thyroid stimulation, both functionally (lower serum TSH concentrations) and anatomically (increased thyroid volume). Although the association between maternal hypothyroidism and increased perinatal morbidity has been described for over a century, more recently, even the presence of anti-thyroid antibodies has been associated with adverse pregnancy outcomes, such as recurrent abortions and placental abruption. This is of major clinical significance, as anti-thyroid antibodies are surprisingly prevalent in pregnancy, especially during the first two trimesters.