Elevated Serum TSH Levels and TPOAb Positivity in Early Pregnancy are Associated with Increased Risk of Hypertensive Disorders of Pregnancy: A Prospective Cohort Study

<b>Background:</b> The relationship between maternal thyroid-stimulating hormone (TSH), free thyroxine (FT4) and thyroid peroxidase antibody (TPOAb) status and hypertensive disorders of pregnancy (HDP) remains uncertain. <b>Methods:</b> This was a prospective cohort study based on the China Birth Cohort Study (CBCS). 36,256 women were included at 6 to 13⁺⁶ gestation from February 2018 to December 2020. Generalized linear mixed models were used to investigate the association between thyroid function and HDP/BP. We further performed multiple subgroup analyses to test the robustness of this association. <b>Results:</b> The final study population was 25,608, and the overall incidence of HDP was 8.0%. After adjusting for maternal age, pre-pregnancy BMI, education, household annual income, smoking status, conception method and parity, the odds of HDP increased by 3.0% with a 1-unit increase in TSH (OR 1.03, 95% CI 1.04-1.06). Maternal TSH and TPOAb positivity were associated with a higher risk of preeclampsia or eclampsia but not gestational hypertension (TSH: OR 1.04, 95% CI 1.01-1.07; TPOAb positivity: OR 1.30, 95% CI 1.09-1.56). TSH and TPOAb positivity were significantly and positively associated with systolic pressure (TSH: β 0.02, 95% CI 0.07-0.26; TPOAb positivity: β 0.02, 95% CI 0.12-0.98) and diastolic pressure (TSH: β 0.02, 95% CI 0.02-0.17; TPOAb positivity: β 0.02, 95% CI 0.06-0.75). Subgroup analyses suggested that the association between TSH and diastolic pressure was stronger in those with BMI ≥ 25 kg/m² (<i>P</i> = 0.014). <b>Conclusions:</b> Our founds suggest that high TSH and TPOAb positivity in the first trimester are associated with an increased risk of preeclampsia or eclampsia.