Do Maternal Antithyroid Antibodies Increase the Risk of Miscarriage?

By John Schnorr, MD

Among all the areas of Reproductive Endocrinology, recurrent pregnancy loss tends to be one of the more controversial areas in regards to the evaluation and treatment for patients with this issue. Part of that is due to the emotional nature of the diagnosis and as a result, the difficulty in truly randomizing patients to different forms of treatment. Consensus opinion, based upon studies is that hypothyroidism can be a cause of miscarriage. There is some controversy about subclinical hypothyroidism and its role, however most Reproductive Endocrinologists would agree that subclinical hypothyroidism should be evaluated and treated with low dose Levothyroxine treatment.

The question then becomes what do we recommend for patients with normal TSH levels, but elevated antithyroid antibodies? Some larger studies conclude that elevated antithyroid antibodies cause miscarriages while others disagree. I found the answer in a large study published in Fertility Sterility in July of 2018 that observed women between 2004 and 2015 who miscarried fetuses with an abnormal number of chromosomes. The key to this study was they only looked at these types of miscarriages which helped to eliminate the “noise” of aneuploidy in the investigations. The study consisted of 74 subjects who had 130 subsequent miscarriages and looked at the prevalence of maternal antithyroid antibodies and compared that to the TSH and T4 thyroid levels. The study found no significant difference in the miscarriage rate between those patients with elevated antithyroid antibodies and those with normal antithyroid antibodies.

The conventional recurrent pregnancy loss evaluation should involve an evaluation of the uterus and the uterine septum to scan for fibroids. In addition, testing should be performed to find out if there is a decreased number of eggs along with acquired blood clot testing including testing for autoimmune antibodies. Progesterone supplementation to prevent miscarriage is controversial in the medical literature, but well received by the patients. Some practitioners administer progesterone in the luteal phase prior to the first sign of pregnancy. The challenge is to make sure it’s started after ovulation or it can be a cause of infertility.