Is Thyroid Replacement Therapy Necessary in Fertility Patients with “Normal” TSH?

Abstract

Thyroid diseases are very common disorders in women, and thyroid hormones are crucial players in many aspects of fetal growth and neurodevelopment, both of which are dependent on an adequate supply of maternal thyroid hormones from early gestation onwards. It is therefore very important to keep women euthyroid during gestation. Globally, hypothyroidism is still frequently caused by iodine deficiency. In iodine sufficient areas, the most common cause of hypothyroidism is thyroid autoimmunity with positive anti-thyroperoxidase antibodies (anti-TPO) measurable in serum. It is well known that overt maternal and fetal hypothyroidism must be avoided during gestation as well as before assisted fertility. It is, however, less clear if milder forms or subclinical hypothyroidism requires thyroxine replacement therapy. Screening for thyroid disease is not recommended by guidelines, but case finding based on specific criteria form general practice among endocrinologists and fertility specialists. There are many different factors to be aware of including, how measurements and interpretations of the laboratory tests for thyroid related hormones are complicated by a combination of changes due to the physiology of pregnancy, and the difficulty of laboratory measurements to correct for these changes. A pragmatic algorithm for the management has been suggested, but there are still many inconsistencies and controversies in the field. Very importantly, all clinicians managing thyroid diseases should be aware of this and discuss it with the female patients of fertile age as soon as the diagnosis of hypothyroidism is made in order to avoid negligence from the patient if she becomes pregnant.