The Reference Intervals of Thyroid Hormones for Pregnant Women in Zhejiang Province.

Gestation-specific reference intervals for thyroid hormones are used to estimate thyroid function in pregnant women. This study was to establish the reference intervals for pregnant women in Zhejiang province, China. A total of 9038 cases were recruited. The values of thyroid-stimulating hormone (TSH), free thyroxine, free triiodothyronine, total thyroxine, and total triiodothyronine were determined by Beckman Coulter DxI-800 analyzers. Our results indicated that the level of TSH declined in the first trimester and then rose as pregnancy progressed. Conversely, the level of free triiodothyronine rose in the first trimester and then declined. The ranges of free thyroxine kept the decreasing trend crossing the gestation period. For total triiodothyronine, the ranges increased as pregnancy progressed and declined in the third trimester. The variation trends of total triiodothyronine and total thyroxine were similar. Our data confirmed the importance of the reference intervals of thyroid hormones for pregnant women.