Before and during pregnancy the thyroid gland and gonadal axes interact continuously. During reproductive life, normal levels of thyroid hormones are required for the maturation of oocytes. Hypothyroidism influences ovarian function by decreasing levels of sex-hormone-binding globulin and increasing the secretion of prolactin. In women of reproductive age, L-thyroxine therapy reverses hypothyroidism improving fertility and avoiding the need for use of assisted reproduction technniques. Infertile women undergoing medically assisted reproduction technologies are treated with a controlled ovarian hyperstimulation to increase circulating estrogen concentrations, which can, on the other hand, severely impair thyroid function. These changes are transient in healthy women, but in women affected by autoimmune thyroid diseases, estrogen stimulation might lead to an altered thyroid function during pregnancy. The frequency of thyroid autoimmunity is raised in infertile women with ovulatory dysfunction and endometriosis whereas hypothyroidism associated with infertility seems to be increased only in women with ovulatory dysfunction. Presence of thyroid autoimmunity does not interfere with normal embryo implantation, but is associated with a significantly raised frequency of miscarriages, even when thyroid function is apparently normal. Subclinical and overt hypothyroidism is associated with an increased risk of pregnancy-related morbidity, for which L-thyroxine therapy is required. Systematic screening for thyroid disorders in pregnant women is still controversial but can be considered an adjunctive tool in women at high risk, particularly infertile women.
25 - 29 Apr 2009
European Society of Endocrinology