Associations between Oxidative/Nitrosative Stress and Thyroid Hormones in Pregnant Women—Tainan Birth Cohort Study (TBCS)

Oxidative and nitrosative stress have been linked to thyroid function in both animal and human studies. In the present study, the associations between oxidative and nitrosative stress and thyroid hormones were investigated. Measurements were obtained from 97 Taiwanese pregnant women at the first, second, and third trimesters. Levels of five oxidative and nitrosative stress biomarkers (8-hydroxy-2′-deoxyguanosine [8-OHdG], 8-nitroguanine [8-NO(2)Gua], 4-hydroxy-2-nonenal-mercapturic acid [HNE-MA], 8-isoprostaglandin F2α [8-isoPGF(2α)], and malondialdehyde [MDA]) were measured using urine samples, and levels of five thyroid hormones (triiodothyronine [T(3)], thyroxine [T(4)], free T(4), thyroid-stimulating hormone [TSH], and T(4)-binding globulin [TBG]) were measured in blood samples. Multiple linear regressions and linear mixed-model regressions were conducted to determine the associations between oxidative or nitrosative stress biomarkers and thyroid hormones in pregnant women. We found that TSH was negatively and significantly associated with 8-NO(2)Gua (−14%, 95% CI [−26.9% to −1.1%]) and HNE-MA (−23%, 95% CI [−35.9% to −10.0%]) levels. However, T(4) (3%, 95% CI [0.2%–5.8%]) and free T(4) (4.3%, 95% CI [0.8%–7.8%]) levels were positively and significantly associated with 8-NO(2)Gua. The T(4) to TBG and free T(4) to TBG ratios were positively and significantly associated with 8-NO(2)Gua level (T(4)/TBG: 3.6%, 95% CI [0.5%–6.7%]; free T(4)/TBG: 5.6%, 95% CI [0.2%–11.1%]). However, the TSH to T(4) ratio was negatively and significantly associated with 8-NO(2)Gua level (−17.3%, 95% CI [−30.4% to −4.3%]). The T(3) to TSH ratio was positively and significantly associated with HNE-MA level (25.2%, 95% CI [11.2%–39.2%]). However, the TSH to T(4) and TSH to free T(4) ratios were negatively and significantly associated with HNE-MA level (TSH/T(4): −21.2%, 95% CI [−34.5% to −7.8%] and TSH/free T(4): −24.0%, 95% CI [−38.3% to −9.6%]). Our findings suggest that an imbalance of oxidative and nitrosative stress may alter thyroid hormone homeostasis during pregnancy. Disruption of the maternal thyroid homeostasis during pregnancy would affect embryonic and fetal development.