In Reply We were pleased to read the letter from the Rotterdam Thyroid Center, and we thank Dr Korevaar and colleagues for their comments in response to our recent publication.1
Currently, in the absence of a laboratory trimester-specific reference range for thyroid-stimulating hormone (TSH) levels, the guidelines recommend a fixed upper limit of 2.5 mIU/L for first trimester and 3.0 mIU/L for second and third trimesters of pregnancy.2 Implementation of a fixed cutoff rather than a population-based cutoff for TSH levels could lead to overdiagnosis of subclinical hypothyroidism in pregnancy and to subsequent overtreatment. As Korevaar et al point out, the reference range for TSH and free thyroxine vary with geography and ethnic origin.3,4 With multiple population-based studies showing an upper trimester–specific TSH limit higher than 2.5 or 3 mIU/L,4 the current fixed cutoff TSH levels seem problematic.
Maraka S, Ospina NS, Montori VM. Subclinical Hypothyroidism Overdiagnosis in Pregnant Women—Reply. JAMA Intern Med. 2015;175(11):1873. doi:10.1001/jamainternmed.2015.5553