The thyroid is a butterfly-shaped gland that lies at the base of the neck and controls the body’s metabolism. It is important for energy production, growth and development, mental function, and proper digestion. In the first 12 weeks of pregnancy, a baby relies on its mother’s thyroid for it’s own metabolism and growth. For this reason, a thorough assessment of thyroid function in women struggling with infertility or chronic miscarriage is essential.
The most common thyroid marker measured is Thyroid Stimulating Hormone (TSH). This hormone is released from the brain, binds to the thyroid gland tissue, and tells the gland to produce the thyroid hormones T3 and T4.
Most labs consider a TSH value below 5 mIU/L or below 4 mIU/L normal. Research, however, has suggested that for optimal fertility outcomes a TSH between 1-2.5 mIU/L is a better target (1). For couples struggling to conceive, getting TSH values in this tighter range has been associated with improved pregnancy numbers and shorter time to conception (2). Additionally, in women undergoing IVF or ICSI who have elevated TSH, treatment with thyroid replacement has been associated with improved embryo quality and pregnancy outcomes (3).
Another important thyroid marker that should be considered in fertility is the presence of antibodies. There are two antibodies that are commonly elevated in hypothyroidism, anti-thyroglobulin (Anti-TG) and anti-thyroid peroxidase (Anti-TPO). Research has found an association between elevated thyroid antibodies and reduced fertility as well as increased miscarriage rates (4). When elevated antibodies are detected, treatment with thyroid hormones has been found to significantly reduce miscarriage risk and the risk of pre-term birth (5).
For women who are dealing with infertility or multiple miscarriages I recommend running a full thyroid panel to get a more comprehensive look at thyroid function and potential risk factors.
(1) Orouji Jokar, T., Fourman, L., Lee, H., Mentzinger, K., & Fazeli, P. (2017). Higher TSH Levels Within the Normal Range Are Associated With Unexplained Infertility. The Journal Of Clinical Endocrinology & Metabolism, 103(2), 632-639. doi: 10.1210/jc.2017-02120.
(2) Yoshioka, W., Amino, N., Ide, A., Kang, S., Kudo, T., & Nishihara, E. et al. (2015). Thyroxine treatment may be useful for subclinical hypothyroidism in patients with female infertility. Endocrine Journal, 62(1), 87-92. doi: 10.1507/endocrj.ej14-0300
(3) Kim, C., Ahn, J., Kang, S., Kim, S., Chae, H., & Kang, B. (2011). Effect of levothyroxine treatment on in vitro fertilization and pregnancy outcome in infertile women with subclinical hypothyroidism undergoing in vitro fertilization/intracytoplasmic sperm injection. Fertility And Sterility, 95(5), 1650-1654. doi: 10.1016/j.fertnstert.2010.12.004
(4) Unuane, D., Velkeniers, B., Anckaert, E., Schiettecatte, J., Tournaye, H., Haentjens, P., & Poppe, K. (2013). Thyroglobulin Autoantibodies: Is There Any Added Value in the Detection of Thyroid Autoimmunity in Women Consulting for Fertility Treatment?. Thyroid, 23(8), 1022-1028. doi: 10.1089/thy.2012.0562
(5) Thangaratinam, S., Tan, A., Knox, E., Kilby, M., Franklyn, J., & Coomarasamy, A. (2012). Association Between Thyroid Autoantibodies and Miscarriage and Preterm Birth. Obstetric Anesthesia Digest, 32(2), 87-88. doi: 10.1097/01.aoa.0000414067.82440.e6