It is well Known that normal pregnancy is accompanied by a rise in the serum concentrations of thyroxine-binding globulin (TBG) and human chorionic gonadotropin (hCG). Alterations of biochemical parameters of thyroid function are recognized
during
gestation and sensitive tests to evaluate the alterations easily are required. Therefore, a cross-sectional study was undertaken in 140 healthy pregnant women to evaluate the efficacy of free T4 measured by 2-step RIA compared to other thyroid
function
tests and to confirm the changes of thyroid function according to the stages of normal pregnancy.
The sensitivities of free T4 index, free T4 (by 2-step RIA), T3 and TSH were realtively high (99.3%, 93.6%, 92.9%, 83.6%, respectively) compared to those of T4 and T3 bead upgake (49.3%, 21.4%) during all stages of pregnancy. There were positive
correlations between free T4 index and free T4 or total 4 (r=0.68, r=0.72; p<0.001). The values of free T4 index sharply decreases from 3.22±0.10 (meam±SEM) during 6th-12th week to an plateau after 16th-20th week of gestation (p<0.01). The
serum
concentrations of free T4 and T3 bead uptake also significantly decreased from 1.65±0.05 ng/dl, 24.7±0.7% during 6th-12th week to an plateau after 16th-20th week of gestation, respectively (p<0.001). No differences were found in the changes of
serum
concentrations of T3, T4 and TSH according to the stages of pregnancy.
In conclusion, it is adequate to measure some tests including free T4 index and free T4 to evaluate thyroid function during pregnancy. The thyroid physiology and changes of thyroid function according to the stages of pregnancy should be
considered
in
the interpretation of thyroid function status during pregnancy. (J Kor Soc Endocrinol 9:183-189, 1994)
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