High thyroid hormone sensitivity is associated with the risk of hypertensive disorders during pregnancy in euthyroid women: the mediating role of triglycerides

Background Few studies have focused on the relationship between thyroid hormone sensitivity and hypertensive disorders of pregnancy (HDP) in euthyroid women. This study aimed to investigate this association among euthyroid pregnant women and the potential mediating effects of serum lipids. Methods This study was conducted at Zhoushan Maternal and Child Health Hospital, Zhejiang Province. The general sociodemographic characteristics and lifestyle behaviors of the participants were collected. Blood pressure was measured during pregnancy. Thyroid function data were extracted from medical records. GEE and logistic regression were applied to assess the associations of thyroid hormone sensitivity with longitudinal BP changes and HDP risk, respectively. A nested case‒control study was further adopted to validate the relationship and explore the mediating effects of serum lipids. Results Among the 4,041 pregnant women, 92 developed HDP. Early-pregnancy FT3/FT4 was positively associated with longitudinal increases in SBP (β = 14.78, P  < 0.001) and DBP (β = 6.76, P  < 0.001). The TFQI was negatively associated with SBP (β= -1.05, P  = 0.003). The mid-pregnancy FT3/FT4 ratio was strongly associated with SBP (β = 14.74, P  < 0.001) and DBP (β = 7.71, P  < 0.001). In contrast, higher mid-pregnancy TFQI, TT4RI, and TSHI were associated with decreased SBP (TFQI: β=-1.96, P  < 0.001; TT4RI: β=-0.07, P  < 0.001; TSHI: β=-1.07, P  < 0.001). Moreover, early-pregnancy FT3/FT4 was associated with increased HDP risk (OR = 27.23, 95% CI: 1.83–406.26). A similar association was found in mid-pregnancy (OR = 38.93, 95% CI: 4.26–355.49). Higher mid-pregnancy TT4RI, TSHI, and TFQI were associated with reduced HDP risk (TT4RI: OR = 0.96, 95% CI: 0.93–1.00; TSHI: OR = 0.65, 95% CI: 0.43–0.99; TFQI: OR = 0.48, 95% CI: 0.27–0.85). Mediation analysis indicated that TG mediated 18.7% of the FT3/FT4-HDP associations (β = 0.153, 95% CI: 0.018–0.390, P  = 0.008) and 15.4% of the TFQI-HDP associations (β=-0.031, 95% CI: -0.068–0.000, P  = 0.026). Conclusions In euthyroid pregnant women, high thyroid hormone sensitivity is associated with an increased risk of HDP. TGs mediate the associations between thyroid sensitivity (FT3/FT4 ratio and TFQI) and HDP. Trial registration: not applicable