Thyroid-Stimulating Hormone Levels within the Trimester-Specific Reference Intervals Are Correlated with Non-High-Density Lipoprotein Cholesterol and Remnant Cholesterol Concentrations in Pregnant Women.

Objective: Thyroid-stimulating hormone (TSH) levels are associated with serum lipid concentrations in the general nonpregnant population. Here, we aimed to establish trimester-specific reference intervals and to explore the associations of their variations within the specific reference intervals during pregnancy.

Methods: Trimester-specific reference intervals were established according to the Clinical and Laboratory Standard Institute EP28-A3c guidelines using a direct sampling method based on a large prospective cohort. After making one-to-one matches, correlation analyses between TSH and lipid index levels, especially within the reference intervals, were conducted.

Result: A total of 1648 pregnant women for TSH and 2045 subjects for lipids were recruited to establish the trimester-specific reference intervals. The upper reference limit (90% confidence interval) of TSH for pregnant women in the first trimester is 3.95 (3.66-4.29) mIU/L, which is very close to the default value (4.0 mIU/L) recommended by the American Thyroid Association in 2017. Apart from triglyceride and high-density lipoprotein cholesterol, TSH levels were positively associated with the serum concentrations of total cholesterol, low-density lipoprotein cholesterol, non-high-density lipoprotein cholesterol (non-HDL-C), and remnant cholesterol (RC) either in the entire range or within the specific reference intervals. Of note, the positive correlations between TSH and non-HDL-C and RC were, albeit similarly weak (r < 0.25), relatively more robust (P < .001).

Conclusion: In this study, we showed positive correlations between TSH and lipid components within trimester-specific reference intervals, highlighting the need for the integrated management of pregnant women over age 35 and with nonoptimal lipid status in China.