Amniotic fluid reverse triiodothyronine in complicated pregnancy.

The concentrations of reverse triiodothyronine (3,3',5'-T3 or rT3) in amniotic fluid (AF) were measured by radioimmunoassay in 81 patients with various complications of pregnancy and in 39 normal pregnant patients at equivalent gestational age. In normal pregnancy, AFrT3 concentrations decreased with advancing gestational age. At 21-25, 26-30, 31-35, and 36-40 weeks of normal pregnancy, AFrT3 concentrations (mean +/- SE) were 353 +/- 62 (n = 6), 131 +/- 49 (n = 7), 94 +/- 25 (n = 14), and 93 +/- 5 (n = 20) ng/dl, respectively (ranges: 200-600, 57-350, 66-135, and 50-135). Both normal and supranormal values of AFrT3 were found in patients with complicated pregnancy. In patients with RH isoimmune disease, higher than normal AFrT3 concentrations were associated with seriously affected or gravely ill fetuses wheras normal AFrT3 concentrations predicted a more favorable outcome. There was a good correlation between AFrT3 and AF pigment (deltaOD450) levels (r = 0.70, P less than 0.001). In complicated pregnancy other than erythroblastosis fetalis, AFrT3 concentrations were not of any prognostic significance, and there was no correlation between AFrT3 and lecithin/spingomyelin ratio. The data suggest that AFrT3 determination may help in the assessment of the fetal condition in erythroblastosis fetalis.