Trimester-Specific Changes in Maternal Thyroid Hormone, Thyrotropin, and Thyroglobulin Concentrations During Gestation: Trends and Associations Across Trimesters in Iodine Sufficiency

Trimester-specific T(3), FT(4), TSH, and Tg concentrations were significantly different between the first and third trimesters (all p < 0.05); second and third trimester values were not significantly different for FT(4), TSH, and Tg (all p > 0.25) although T3 was significantly higher in the third, relative to the second trimester. T(4) was not significantly different at any trimester (all p > 0.80). With two exceptions, analyte concentrations tended not to be correlated at each trimester and at 1-year postpartum. One exception was that T(3) and T(4) tended to be associated (all p < 0.05) at all time points except the third trimester (rho = 0.239, p > 0.05). T(4) and FT(4) concentrations tended to correlate positively during pregnancy (rho 0.361-0.382, all p < 0.05) but not postpartum (rho = 0.179, p > 0.05). Trends suggest that trimester-specific measurements of T(3), FT(4), Tg, and possibly TSH are warranted.