Radioimmunoassay of thyroxine and 3,3',5'-triiodothyronine (reverse T3) in human amniotic fluid.
Measurement of amniotic fluid iodothyronine concentrations may enable antenatal detection of fetal thyroid abnormalities; however, the delineation of normal ranges is complicated by methodological problems associated with strong and highly variable protein-binding, and specificity of antisera. Improved radioimmunoassays of thyroxine (T4) and 3,3',5-triiodothyronine (reverse T3, rT3) have been developed to overcome these problems. In normal pregnancy, mean rT3 concentrations at less than 17 weeks, 17-22 weeks and 35-42 weeks gestation were 3.6 nmol/l (n = 21), 6.1 nmol/1 (n = 14) and 0.66 nmol/1 (n = 39) respectively; corresponding mean T4 concentrations were 2.4 nmol/1, 6.5 nmol/1 and 3.6 nmol/1. rT3 concentrations showed a strong positive correlation with T4 concentration in each age range; however, the molar ratio of rT3:T4 decreased progressively with gestational age, from 1.69 at less than 17 weeks to 0.19 at 35-42 weeks. In both mid- and late gestation, rT3 and T4 concentrations were strongly correlated with total amniotic fluid protein concentrations.
D000653:Amniotic Fluid / Q000032:analysis*; D005260:Female; D006801:Humans; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D011506:Proteins / Q000032:analysis; D011863:Radioimmunoassay; D013974:Thyroxine / Q000032:analysis*; D014284:Triiodothyronine / Q000032:analysis*; D014285:Triiodothyronine, Reverse / Q000032:analysis*
D011506:Proteins; D014284:Triiodothyronine; D014285:Triiodothyronine, Reverse; D013974:Thyroxine