Evaluation of plasma iodothyronines in various stages of pregnancy

Evaluation of thyroid status during the whole normal pregnancy was carried out by measuring serum total thyroxine (TT4), total 3,5,3' triiodothyronine (TT3), T3 resin uptake (T3(U)), 3,3',5' triiodothyronine (rT3), free thyroxine index (FTI), free thyroxine (FT4) and thyrotrophin (TSH) in 70 serum samples from 42 pregnant women being in a variable period from the 6th to the 40th week of pregnancy and in 14 serum samples from 14 non pregnant healthy women. The serum samples were divided in 7 groups, according to the gestational age of the subjects. Every group was formed by 10 samples collected within the same five weeks period. The levels of TT4, TT3, T3 (U) and rT3 were found significantly elevated during pregnancy, above the levels of the control group (p less than 0.01); the increase is very early. FTI remained in the range of normal non pregnant subjects without any significant change in all groups studied. FT4 concentration showed a progressive downward trend with gestational age. This fall became significant in the second group (11th to 15th weeks), when compared to the levels of non pregnant women (p less than 0.01) TSH mean values remained in the normal range within the three trimesters, though they showed some fluctuations.