<b>Association between maternal thyroid function in early pregnancy and hypertensive disorders of pregnancy: a prospective cohort study</b>

Context: Hypertensive disorders of pregnancy (HDP) are linked with a variety of maternal and fetal complications. Numerous observational studies have examined the correlation between thyroid function and the incidence of HDP, with conflicting results. Objective: Our aim was to explore the correlation between thyroid function tests in early pregnancy, and the risk of HDP. Design: This research constitutes a prospective cohort study based on the China Birth Cohort Study (CBCS), from February 2018 to December 2020. Setting: A tertiary maternal and child health hospital. Participants: A total of 36,256 subjects from February 2018 to December 2020 were selected based on CBCS. Main Outcome Measures: Hypertensive disorders of pregnancy. Results: After application of the exclusion criteria, the final study population was 24,364 pregnant women and the prevalence of HDP was 8.77%. In the fully adjusted model (Model 3), thyroid-stimulating hormone (TSH) was significantly and positively correlated with HDP (odds ratio (OR) 1.034, 95%CI 1.007,1.063). Compared to the lowest quartile(reference), both the highest full-range and normal-range TSH quartiles significantly increased the risk of HDP (OR 1.219, 95% CI 1.072,1.387; OR 1.241, 95% CI 1.087,1.417, respectively), and all P for trend<.001. Based on restricted cubic spline, we identified a nearly linear correlation between the full range of TSH and risk of incident HDP (P for overall < 0.001, P for nonlinear=0.065). No significant association were found between free thyroxine (FT4), thyroid peroxidase antibody (TPOAb) positivity and the prevalence of HDP. Conclusions: High TSH might be associated with increased risk of HDP.</p