Different Thyroidal Responses to Human Chorionic Gonadotropin Under Different Thyroid Peroxidase Antibody and/or Thyroglobulin Antibody Positivity Conditions During the First Half of Pregnancy

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Abstract
Background: Thyroid peroxidase antibody (TPOAb) positivity can attenuate gestational thyroid responses to human chorionic gonadotropin (hCG) during pregnancy, whereas the effects of thyroglobulin antibodies (TgAb) remain unknown. The aim of our study was to explore the thyroid response to hCG in women with thyrotropin (TSH) levels within the method-specific reference range under different conditions of thyroid autoimmunity. Methods: The study screened 822 women at 7–20 weeks of gestation using the pregnancy-specific reference range for TSH. Serum TSH, free thyroxine (fT4), TPOAb, TgAb, and β-hCG levels were measured using electrochemiluminescence immunoassays. Results: The enrolled pregnant women were subdivided into four subgroups based on TPOAb/TgAb positivity: co-positive for TPOAb and TgAb (group 1), isolated TPOAb positive (group 2), isolated TgAb positive (group 3), and co-negative for TPOAb and TgAb (group 4). TSH was negatively associated with hCG in all four groups ( p < 0.05). fT4 was positively associated with hCG in groups 3 and 4 ( p < 0.01) but not in groups 1 ( p = 0.096) and 2 ( p = 0.758). Group 2 was further stratified into tertiles according to TPOAb concentrations. No negative TSH/hCG association was observed in the middle- and upper-tertile groups when TPOAb were ≥53 IU/mL ( p > 0.05). There was no positive fT4/hCG association in any of the three subgroups ( p > 0.05). Similarly, group 3 was further stratified into tertiles according to TgAb levels. TSH was negatively associated with hCG in the lower and middle tertiles ( p < 0.01), but the association was not found in the upper tertile when TgAb was ≥356 IU/mL ( p = 0.191). fT4 was positively associated with hCG in the lower tertile ( p = 0.027) but not in subgroups when TgAb was ≥219 IU/mL ( p > 0.05). Conclusions: When TSH was within the pregnancy-specific reference range, high concentrations of TPOAb and TgAb attenuated the fT4 stimulation and suppression of TSH by hCG. The results imply that TgAb, in addition to TPOAb, could also interfere with thyroidal responses to hCG during the first half of pregnancy.

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