Measurement of thyroid-stimulating hormone in human amniotic fluid.

TSH was measured in human amniotic fluid after 3- to 8-fold concentration of the fluids. Amniotic fluid TSH was identical to standard pituitary TSH by immunological and gel chromatographic criteria. In 201 samples of normal second trimester amniotic fluid (16-19 weeks of pregnancy), amniotic fluid TSH concentrations had a mean value of 0.4 microunits/ml (range, less than 0.15 to 1.7 microunits/ml). In 21 samples of third trimester amniotic fluid (obtained to check fetal lung maturity), amniotic fluid TSH concentrations had a mean value of 0.25 microunits/ml (range, less than 0.15 to 0.55 microunits/ml). The capability of measuring TSH in amniotic fluid and the relative constancy of these values between the second and third trimesters of pregnancy suggest that the determination of TSH levels in amniotic fluid may be useful in the diagnosis of fetal hypothyroidism in utero.