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?

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.