Impact of thyroid disease on fertility and assisted conception

Thyroid autoimmunity (TAI) and/or thyroid dysfunction are prevalent in women of reproductive age and have independently been associated with adverse fertility and pregnancy outcomes, in the case of spontaneous conception or after assisted reproductive technology (ART). Thus, it seems reasonable to screen for thyrotropin (TSH) and thyroid peroxidase autoantibodies (TPO-abs) in infertile women attempting pregnancy. However, even if the relationship between fertility and thyroid dysfunction and/or TAI persists when properly controlled for other variables, it remains challenging to claim causation. Several studies with different designs (cross sectional, case -control, prospective and retrospective cohort studies) have looked at the association between thyroid autoimmunity, thyroid function and fertility. Heterogeneity among study results are related to small numbers of included patients, poor study design, selection of causes of infertility and different assays used to measure TAI, thyroid hormones and TSH reference values. Indeed, there is no consensus regarding the upper limit of normal for TSH to define thyroid dysfunction and the cut-off levels for intervention. Furthermore, data from interventional trials looking at the impact of levothyroxine treatment on fertility outcome in randomised controlled studies are scarce. Despite the recent update of the guidelines by the American Thyroid Association (ATA) for the Diagnosis and Management of Thyroid Disease during Pregnancy and the postpartum, many questions remain unsettled in ART.