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Figure 14-8 Upper left panel: pattern of changes in serum TBG concentrations (mean + sd) in 606 normal pregnant women ( Ref 1). Upper right panel: pattern of changes in serum total T4 concentrations (individual results) in 98 normal pregnancies ( Ref 60). Middle panel: free T4 measurements in 29 women in the 9th month of gestation, using equilibrium dialysis (ED), and 9 different immunoassays (EL: Elecsys; VD: Vidas; VT: Vitros ECi; GC: Gamma-Coat; IM: Immunotech; AD: Advantage; AX: AxSYM; AC: ACS: 180; AI: AIA Pack). The boxes show the non-pregnant upper and lower reference intervals. The percentages given in the upper part of the figure show the mean decrement (in percent) of serum free T4 values compared with the mean free T4 reference value for non-pregnant subjects, provided by the manufacturer. It can be seen that free T4 values were decreased by 40% when measured by ED, and by 17-34% depending on the immunoassay employed . Lower left panel: pattern of changes in serum free T4 concentrations (individual results) in 98 normal pregnancies in the USA, with an adequate iodine intake . Lower right panel: pattern of changes in serum free T4