Between 2% and 5% of women of the childbearing age have reduced thyroid hormone activity (hypothyroidism). Women with hypothyroidism often manifest with reproductive failure i.e. infertility, unexplained (often repeated) IVF failure, or recurrent pregnancy loss (RPL). The condition is 5-10 times more common in women than in men. In most cases hypothyroidism is caused by damage to the thyroid gland resulting from of thyroid autoimmunity (Hashimoto’s disease) caused by damage done to the thyroid gland by antithyroglobulin and antimicrosomal auto-antibodies. 

The increased prevalence of hypothyroidism and thyroid autoimmunity (TAI) in women is likely the result of a combination of genetic factors, estrogen-related effects and chromosome X abnormalities.  This having been said, there is significantly increased incidence of thyroid antibodies in non-pregnant women with a history of infertility and recurrent pregnancy loss and thyroid antibodies can be present asymptomatically in women without them manifesting with overt clinical or endocrinologic evidence of thyroid disease. In addition, these antibodies may persist in women who have suffered from hyper- or hypothyroidism even after normalization of their thyroid function by appropriate pharmacological treatment. The manifestations of reproductive dysfunction thus seem to be linked more to the presence of thyroid autoimmunity (TAI) than to clinical existence of hypothyroidism and treatment of the latter does not routinely result in a subsequent improvement in reproductive performance.

It follows, that if antithyroid autoantibodies are associated with reproductive dysfunction they may serve as useful markers for predicting poor outcome in patients undergoing assisted reproductive technologies.

Some years back, I reported on the fact that 47% of women who harbor thyroid autoantibodies, regardless of the absence or presence of clinical hypothyroidism, have activated uterine natural killer cells (NKa) cells and cytotoxic lymphocytes (CTL) and  that such women often present with reproductive dysfunction. We demonstrated that appropriate immunotherapy with IVIG or intralipid (IL) and steroids, subsequently often results in a significant improvement in reproductive performance in such cases.

The fact that almost 50% of women who harbor antithyroid antibodies do not have activated CTL/NK cells suggests that it is NOT the antithyroid antibodies themselves that cause reproductive dysfunction. The activation of CTL and NK cells that occurs in half of the cases with TAI is probably an epiphenomenon with the associated reproductive dysfunction being due to CTL/NK cell activation that damages the early “root system” (trophoblast) of the implanting embryo. We have shown that treatment of those women who have thyroid antibodies + NKa/CTL using IL/steroids, improves subsequent reproductive performance while women with thyroid antibodies who do not harbor NKa/CTL do not require or benefit from such treatment.