Association between maternal circulating total triiodothyronine and subsequent risk of preeclampsia

Abstract Introduction To clarify the uncertain association between maternal total triiodothyronine (TT3) levels and preeclampsia risk. Methods In a hospital-based cohort of pregnant women with universal thyroid testing, we assessed the association between TT3 and preeclampsia using directed acyclic graphs (DAG) to control confounders. Results Maternal TT3 levels were associated with preeclampsia risk, with an adjusted odd ratio (OR) of 2.32 (95% confidence interval (CI) 2.02–2.68) in women with the highest TT3 quartile comparing to those in the lowest quartile. A J-shaped association was identified for early onset preeclampsia, with particularly strong association when thyroid-stimulating hormone exceeded 2.5 μIU/mL (OR, 17.22, 95% CI 4.52–65.60). Gestational age > 18 weeks at measurement significantly modified the effect of TT3 on preeclampsia risk, with an interaction OR of 3.22 (95% CI 1.56–6.62). Conclusion Increased maternal TT3 levels were associated with preeclampsia. TT3 may contribute to preeclampsia pathogenesis and serve as a clinical biomarker, especially for early onset cases with thyroid dysfunction.