Over the past twenty years there has been a major expansion of our knowledge regarding thyroid disorders associated with pregnancy. These advances relate to the optimal management of pregnant women who are on l-thyroxine therapy, the impact of iodine deficiency on the mother and developing fetus, the adverse effects of maternal hypothyroidism on mental development in their offspring, thyroid dysfunction associated with postpartum thyroiditis, etc. Simultaneously, a doubling of the miscarriage rate has been reported in studies in antibody-positive euthyroid women, and an increase in preterm delivery has been found in women with subclinical hypothyroidism and/or thyroid autoimmunity. Given the rapidity of advances in this field, it is not surprising that some controversy surrounds the optimal detection and management of thyroid diseases during pregnancy, especially since pregnant women may have a variety of known or undisclosed thyroid conditions (such as hypothyroidism and hyperthyroidism), the presence of thyroid autoantibodies, thyroid nodules, or unsatisfactory iodine nutrition.

Pregnancy may affect the course of thyroid disorders and, conversely, thyroid diseases may affect the course of pregnancy. Moreover, thyroid disorders (and their management) may affect both the pregnant woman and the developing fetus. Finally, pregnant women may be under the care of multiple health care professionals, including obstetricians, nurse midwives, family practitioners, endocrinologists and/or internists, making the development of clinical practice guidelines all the more urgent and critical. Accordingly, an international task force was created under the auspices of the American Endocrine Society to review the best evidence in the field and develop evidence-based guidelines. Members of the task force included representatives from the Endocrine Society, American Thyroid Association (ATA), Association of American Clinical Endocrinologists (AACE), European Thyroid Association (ETA), Asia & Oceania Thyroid Association (AOTA), and the Latin American Thyroid Society (LATS). The task force worked for two years to develop these guidelines that eventually were, in turn, approved by the above-mentioned sponsoring organizations. The work of the task force was finally achieved in 2007 and the final publication of these guidelines is due to take place in August of the present year [1]. The main recommendations, extracted from these guidelines, will be added in the present update of this chapter, under the form of ‘bullet tables’ inserted at the end of each relevant section.