Thyroid hormone levels in maternal and fetal serum during different gestational ages. Data at gestational weeks 12–17, depicted as mean ± SEM, were collected from Calvo et al. [97], which measured concentrations of (free) thyroid hormone and binding proteins in first trimester in amniotic fluids and fetal serum. The other data, depicted as mean ± SD, were from Hume et al. [100], which measured concentrations of (free) thyroid hormone and thyroxine-binding protein during the second and third trimesters in cord blood and the mothers. Note: the data of maternal and fetal FT4 was depicted on the y-axis. TT4: total T4; FT4: free T4; TT3: total T3.