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J Clin Endocrinol Metab. 2014 Jan;99(1):73-9. doi: 10.1210/jc.2013-1674. Epub 2013 Dec 20.

Assessment of thyroid function during first-trimester pregnancy: what is the rational upper limit of serum TSH during the first trimester in Chinese pregnant women?

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The Endocrine Institute and The Liaoning Provincial Key Laboratory of Endocrine Diseases (ChenyanL., Z.S., J.M., W.W., X.X., C.F., W.T.), Department of Endocrinology and Metabolism, The First Hospital of China Medical University, Shenyang, 110001 China; Shenyang Women's and Children's Hospital (W.Z., ChenyangL.), Shenyang, 110011 China; Departments of Obstetrics and Gynecology (B.X.) and Endocrinology (S.Z.), No. 202 Hospital of People's Liberation Army, Shenyang, 110003 China; Dalian Obstetrics and Gynecology Hospital (L.B.), Dalian, 116003 China; Department of Obstetrics and Gynecology (T.M.), The First Hospital of China Medical University, Shenyang, 110001 China; Department of Endocrinology (J.D.), The First Affiliated Hospital of Dalian Medical University, Dalian, China; Department of Endocrinology (Z.G.), Dalian Municipal Central Hospital Affiliated of Dalian Medical University, Dalian, 116033 China; Department of Endocrinology (X.Z.), The First Hospital of Dandong, Dandong, 118000 China; and Shenyang Women and Children Health Care Center (L.Y.), Shenyang, 110032 China.



Guidelines of the American Thyroid Association (ATA) proposed that the upper limit of the TSH reference range should be 2.5 mIU/L in first trimester, but the reported ranges in China are significantly higher.


Our objective was to establish a rational reference range of serum TSH for diagnosis of subclinical hypothyroidism in the first trimester of pregnant women in China.


We screened 4800 pregnant women in the first trimester and 2000 women who planned to become pregnant and evaluated 535 pregnant women in follow-up visits during the second and third trimester.


Median concentrations of serum TSH decreased significantly from the seventh week of gestation. The median of TSH from 4 to 6 weeks was significantly higher than from 7 to 12 weeks (2.15 [0.56-5.31] mIU/L vs 1.47 [0.10-4.34] mIU/L, P<.001); however, there was no significant difference compared with nonpregnant women (2.07 [0.69-5.64] mIU/L; P=.784). The median of free T4 was not significantly altered in the first trimester. The prevalence of subclinical hypothyroidism in the 4800 pregnant women was 27.8% on the diagnostic criteria of TSH>2.5 mIU/L and 4.0% using the reference interval derived by our laboratory (0.14-4.87 mIU/L).Additionally, of 118 pregnant women who had serum TSH>2.5 mIU/L in the first trimester, only 30.0% and 20.3% of them at the 20th and 30th week of gestation had TSH>3.0 mIU/L.


The reference range for nonpregnant women can be used for the assessment of pregnant women at 4 to 6 weeks of gestation. The upper limit of serum TSH in the first trimester was much higher than 2.5 mIU/L in Chinese pregnant women.

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