High frequency of antithyroid autoantibodies in pregnant women at increased risk of gestational diabetes mellitus

Background: Thyroid autoantibodies (ThyAb) and subclinical hypothyroidism o ccur more frequently in pregnant women with insulin-dependent diabetes mell itus than in healthy pregnant women. Few studies have investigated the pres ence of ThyAb in women with gestational diabetes mellitus (GDM), and no sig nificant association between diabetes in pregnancy and thyroid function has been reported. Objective: To assess the thyroid biochemical profile and estimate the preva lence of ThyAb in a group of pregnant women at increased risk of GDM due to family and personal risk factors, and to investigate the relationship betw een a positive family history of diabetes or thyroid diseases and the event ual presence of ThyAb during pregnancy. Methods: Oral glucose tolerance, serum ThyAb and thyroid function were eval uated in 181 pregnant women with increased risk for GDM (study group). Seve nteen healthy pregnant women without risk factors for GDR;I and with a norm al glucose tolerance were recruited as controls. Results: The women who developed GDM showed a mean free thyroxine concentra tion significantly lower than that observed in the healthy pregnant women a nd in those with impaired gestational glucose tolerance and normal glucose tolerance. Twenty-nine of the 181 women in the study group (16%) wore ThyAb positive. However, the risk of being ThyAb positive during pregnancy was t hree times greater in the women with positive family history of both diabet es mellitus and thyroid disease than in those with no family history of the se conditions. Conclusions: This study showed that women with increased risk of GDM, mostl y those with family history of diabetes mellitus and thyroid disease, also have an increased risk of being ThyAb positive during pregnancy. It also hi ghlighted the importance of evaluating thyroid function in pregnant women w ith impaired glucose tolerance, in view of their increased risk of subclini cal hypothyroidism.