A 2010 article in the Journal of Clinical Endocrinology Metabolism (J Clin Endocrinol Metab 95:E44-E48, 2010) reminded us of how important thyroid function is in a healthy pregnancy. The TSH and thyroid peroxidase antibodies are blood tests that we require patients to have prior to beginning fertility treatment and again with a positive pregnancy test.
This study evaluated 4123 thyroid peroxidase antibody negative women with TSH levels under 5.0 mIU/liter who were pregnant (women who were hyperthyroid were excluded from the study). They divided the women in to two groups: Group A had TSH levels under 2.5 mIU/liter and Group B had TSH levels between 2.6 and 5.0 mIU/liter.
What they found was surprising. Group A had a pregnancy loss rate of 3.6% and Group B had a 6.1% rate of pregnancy loss. Statistical analysis showed that this was a signficant difference (P=0.006). There was no difference in the rate of preterm delivery in either group.
This information supports what we have long suspected; it is important that the thyroid be functioning properly and if not, thyroid replacement therapy should be instituted to help prevent pregnancy loss. We also learned that it is important to institute thyroid replacement therapy with TSH levels above 2.5 mIU/liter.