Second-trimester reference intervals for thyroid tests: the role of ethnicity.

Area of Science:

• Endocrinology
• Reproductive Health
• Clinical Chemistry

Background:

• Thyroid function naturally changes during pregnancy, making diagnosis of thyroid disorders challenging.
• Maternal thyroid dysfunction is linked to adverse pregnancy outcomes.
• This study investigates thyroid function test results across different ethnicities in the second trimester.

Purpose of the Study:

• To evaluate thyroid function test results stratified by ethnicity and gestational week during the second trimester of pregnancy.
• To establish ethnic-specific reference intervals for thyroid hormones and antibodies.
• To understand the impact of ethnicity on thyroid autoimmunity and thyroid-stimulating hormone levels in pregnant individuals.

Main Methods:

• Collected 3064 blood specimens from Asian, Black, Hispanic, and White participants.
• Measured thyroid-stimulating hormone (TSH), total and free thyroxine (TT4, FT4), total and free triiodothyronine (TT3, FT3), thyroglobulin autoantibodies (TgAb), and thyroid peroxidase autoantibodies (TPOAb).
• Calculated reference intervals for antibody-negative samples with normal TSH and for thyroid hormones in antibody-negative samples with normal TSH.

Main Results:

• Prevalence of TgAb and TPOAb positivity was highest in Asians (10.6% and 12.4%, respectively) and lowest in Blacks (1.8% and 4.1%, respectively).
• Black individuals exhibited lower prevalences of positive thyroid antibodies and elevated TSH.
• Whites had the highest prevalence of elevated TSH, and Asians showed significantly lower reference limits for TT3.

Conclusions:

• Ethnic variations exist in thyroid antibody positivity and TSH levels during the second trimester of pregnancy.
• Reference intervals for thyroid hormones, particularly TT3, differ among ethnic groups.
• Established reference intervals for pregnant individuals in their second trimester differ from those of nonpregnant individuals.