Comparison of thyroid stimulators and thyroid hormone concentrations in the sera of pregnant women.

To clarify the role of various thyroid stimulators in normal human pregnancy, we measured serum TSH, chorionic TSH (hCT), hCG, bioassayable thyroid-stimulating activity, T4, T3, T3 uptake, free T4 and free T3 indexes, free T4, and free T3 by dialysis in 339 serum samples from pregnant women at various intervals of pregnancy and in 40 normal female controls. Serum T4 and T3 and free T4 and free T3 indexes were significantly elevated throughout pregnancy in comparison with controls. Free T4 concentration was elevated after 10 weeks of pregnancy and free T3 concentration was elevated at 13--20 weeks.