editorials August 01, 2016 August 01, 2016

Are TSH normal reference ranges adequate for pregnant women?

DOI: 10.1590/2359-3997000000182

A) PREANALYTICAL FACTORS

Gestational age – The changes in thyroid function tests according to gestational age have been elegantly shown in a study of 13,599 nulliparous women evaluated at 1 week intervals from the 6^th week to term. The study documented that TSH falls to minimal levels during the 10^th week, followed by a progressive increase until term, with its value in the 10^th week being half the value observed at the beginning of pregnancy. Studies on other populations (Finnish and Chinese) (,) have confirmed these results. Thus, a correct interpretation of thyroid function requires knowledge of gestational age.

Presence of anti-thyroid antibodies – Anti-peroxidase and anti-thyroglobulin antibodies are markers of thyroid autoimmunity. Consistent evidence has shown that women with increased levels of these antibodies tend to have higher TSH concentrations. These observations suggest that women with positive titers of these antibodies should not be included in studies of reference values for healthy controls, a rule that is often ignored.

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