Role of trimester-specific reference intervals of thyroid hormones in evaluating thyroid function during the second trimester of pregnancy

Objective To explore the influence of trimester-specific reference intervals and non-pregnant population reference intervals of thyroid parameters on the interpretation of thyroid function tests in pregnant women during the second trimester of pregnancy.Methods 1121 serum samples of pregnant women who received the screening for Down's syndrome at the 16th to 20th gestational weeks from July 2003 to April 2004 in Shenyang Women and Infants healthcare center were acquired.Serum TSH、TT4、FT4 and TPOAb were measured.Results The prevalence of subclinical hypothyroidism and hypothyroxinemia were 5.89% and 1.52% respectively according to trimester-specific reference intervals.The prevalence of subclinical hypothyroidism and hypothyroxinemia were 1.52% and 0.89% respectively according to non-pregnant population reference intervals.The prevalence of subclincal hypothyroidism or hypothyroxinemia according to the two different reference intervals was significantly different(all P0.001).The missed diagnostic rate of subclinical hypothyroidism and hypothyroxinemia were 4.37% and 0.63% respectively according to non-pregnant population reference intervals.Conclusion The missed diagnostic rate of subclinical thyroid abnormalities during the second trimester of pregnancy may be decreased by applying the trimester-specific reference intervals.