The upper limit for TSH during pregnancy: why we should stop using fixed limits of 2.5 or 3.0 mU/l.

Physiological changes necessitate the use of pregnancy-specific reference ranges for TSH and FT4 to diagnose thyroid dysfunction during pregnancy. Although many centers use fixed upper limits for TSH of 2.5 or 3.0 mU/L, this comment describeds new data which indicate that such cut-offs are too low and may lead to overdiagnosis or even overtreatment. The new guidelines of the American Thyroid Association have considerably changed recommendations regarding thyroid function reference ranges in pregnancy accordingly. Also a stepwise approach to interpreting these guidelines is discussed as well as the relevant role of FT4 in diagnosis.