J Korean Med Sci.  2015 Sep;30(9):1308-1312. 10.3346/jkms.2015.30.9.1308.

Gestational Age-specific Cut-off Values Are Needed for Diagnosis of Subclinical Hypothyroidism in Early Pregnancy

• Kim HS
• Kim BJ
• Oh S
• Lee DY
• Hwang KR
• Jeon HW
• Lee SM

• KMID: 2344157
• DOI: http://doi.org/10.3346/jkms.2015.30.9.1308

Abstract

During the first trimester of pregnancy, thyroid-stimulating hormone (TSH) >2.5 mIU/L has been suggested as the universal criterion for subclinical hypothyroidism. However, TSH levels change continuously during pregnancy, even in the first trimester. Therefore the use of a fixed cut-off value for TSH may result in a different diagnosis rate of subclinical hypothyroidism according to gestational age. The objective of this study was to obtain the normal reference range of TSH during the first trimester in Korean gravida and to determine the diagnosis rate of subclinical hypothyroidism using the fixed cut-off value (TSH >2.5 mIU/L). The study population consisted of pregnant women who were measured for TSH during the first trimester of pregnancy (n=492) and nonpregnant women (n=984). Median concentration of TSH in pregnant women was lower than in non-pregnant women. There was a continuous decrease of median TSH concentration during the first trimester of pregnancy (median TSH concentration: 1.82 mIU/L for 3+0 to 6+6 weeks; 1.53 mIU/L for 7+0 to 7+6 weeks; and 1.05 mIU/L for 8+0 to 13+6 weeks). Using the fixed cut-off value of TSH >2.5 mIU/L, the diagnosis rate of subclinical hypothyroidism decreased significantly according to the gestational age (GA) at TSH (25% in 3+0 to 6+6 weeks, 13% in 7+0 to 7+6 weeks, and 9% for 8+0 to 13+6 weeks, P<0.001), whereas the diagnosis rate was 5% in all GA with the use of a GA-specific cut-off value (P=0.995). Therefore, GA-specific criteria might be more appropriate for the diagnosis of subclinical hypothyroidism.

Keyword

Hypothyroidism; Pregnancy Trimester, First; Thyrotropin; Reference Values

MeSH Terms

Adult
*Algorithms
Biomarkers/blood
Diagnosis, Computer-Assisted/*methods
*Diagnostic Techniques, Obstetrical and Gynecological
Female
*Gestational Age
Humans
Hypothyroidism/blood/*diagnosis
Pregnancy
Pregnancy Complications/blood/*diagnosis
Reproducibility of Results
Republic of Korea
Sensitivity and Specificity
Thyrotropin/*blood
Biomarkers
Thyrotropin

Figure

• 

  Fig. 1 5th, 50th, and 95th percentile of thyroid-stimulating hormone of pregnant women in each gestational age.

• 

  Fig. 2 The prevalence of subclinical hypothyroidism in each gestational age at measurement according to the fixed cut-off value or gestational age specific cut-off value of thyroid-stimulating hormone: The prevalence of subclinical hypothyroidism significantly decreases along with increasing gestational age when using the fixed cut-off value of TSH > 2.5 mIU/L (P < 0.001, chi-square test for trend). However, the prevalence of subclinical hypothyroidism was 5% in all gestational age with the use of GA-specific cut-off value (P = 0.995, chi-square test for trend).

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