Thyroid-Stimulating Hormone Values in Pregnancy: Cutoff Controversy Continues?

Thyroid disorders in pregnancy are important causes of adverse pregnancy outcome. So it is very pertinent that thyroid function is maintained in normal range during pregnancy. Serum thyroid-stimulating hormone (TSH) value is the best indicator for assessing and monitoring thyroid function. The increasing metabolic demands of pregnancy alter the thyroid physiology in early pregnancy; hence, it becomes necessary to define trimester-specific reference range. Several reports and guidelines have been published recommending varied TSH cutoffs in different studies. The most significant guidelines which created controversy about TSH cutoffs was that of American Thyroid Association (ATA) (Stagnaro-Green et al. in Thyroid 21:1081-1125, 2011) followed by Endocrine Society clinical practice guideline (De Groot et al. in J Clin Endocrinol 97:2543-2565, 2012). Both these gave stricter TSH cutoffs as .1 to 2.5 mIU/L in first trimester, .2 to 3.0 mIU/L in second trimester and .3 to 3 mIU/L in third trimester. Subsequently many reports, meta-analysis and systematic reviews were published which recommended higher cutoffs. With due consideration, ATA revised the guidelines in 2017, recommending the upper cutoff limit .5 mIU/L less than the preconception TSH value or as 4.0 mIU/L when local population-specific reference range is not available (Alexander et al. Thyroid 27(3):315-389, 2017). The controversy is not yet completely resolved specially regarding management of subclinical hypothyroidism. This editorial addresses this ongoing controversy.