Thyroid autoimmunity and female gender.

Sexual dimorphism exists in regard to the immune response between women and men, and it accounts for the greater prevalence of thyroid autoimmunity in women. Similarly to the human situation a sex-related susceptibility to autoimmune thyroiditis is evident in animal models. A direct influence of genes on sex chromosomes (X or Y) on the immune response has been postulated in some models of autoimmune thyroiditis in rats. On the other hand sex hormones have been implicated to explain the majority of sex differences in the autoimmune response against the thyroid. A state of immune suppression during pregnancy influences the clinical course of autoimmune thyroid diseases, in that a typical amelioration during pregnancy is accompanied by aggravation following delivery. This immunologic rebound phenomenon may also underly the post partum thyroid dysfunction in otherwise healthy women with a genetic predisposition to autoimmune thyroid disease. Thyroid autoimmunity also interferes with the female reproductive function. Hypothyroidism and less frequently hyperthyroidism due to thyroid autoimmune disorders may produce menstrual dysfunction, anovulation and eventually infertility. Maternal hyper- or hypothyroidism can affect the outcome of pregnancy, producing a higher incidence of miscarriages, maternal complications, and congenital malformations. Untreated maternal hypothyroidism produced by Hashimoto's disease during pregnancy can impair the neurological development of the fetus due to a reduced availability of maternal thyroxine during early gestation.2+ More specifically, fetal and/or neonatal hypo- or hyperthyroidism produced by the transplacental passage of maternal thyroid autoantibodies can impair growth and neuropsychological development of affected children.