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

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 was a prospective cohort study based on the China Birth Cohort Study (CBCS), from February 2018, to December, 2020. Multiple imputation was used to impute missing values for covariates. Setting: A tertiary maternal and child health hospital. Participants: A total of 36,256 women who were pregnant between February, 2018 and December, 2020 were selected using the CBCS. Main Outcome Measures: HDP, gestational hypertension, preeclampsia. Results: We excluded participants with multiple pregnancy, previous thyroid disease, pre-existing hypertension, medication effects on medication affecting thyroid function or blood pressure, or missing data. The final study population was 25,608, and the overall incidence of HDP was 8.74%. After fully adjusting for maternal age, pre-BMI, education, household annual income, smoking status, pregnancy mode and parity, thyroid-stimulating hormone (TSH), but not free thyroxine (FT4) or thyroid peroxidase antibody (TPOAb), was found to be correlated with HDP (odds ratio (OR) 1.04, 95%CI 1.01,1.07). Based on restricted cubic splines, the correlation between the full range of TSH and risk of HDP was determined to be non-linear (P for overall < .0001, P for nonlinear < .0001). Conclusions: High TSH is associated with increased risk of HDP.