Vitamin A and retinol-binding protein in amniotic fluid.

Amniotic fluid and serum samples that had been obtained from mothers at 10 to 33 wk of gestation were analyzed for retinol and retinol-binding protein. No difference was found in serum retinol with advancing gestation. The concentration of retinol in amniotic fluid from 20 wk onward was significantly greater than at 16 to 18 wk. No esters of retinol and no carotenoids were detected in amniotic fluid. Serum and amniotic fluid samples from the same mothers were significantly correlated for retinol (p less than 0.02). Retinol-binding protein, detected by radial immunodiffusion, was found in amniotic fluid in molar excess of, and significantly (p less than 0.001) correlated with, retinol in amniotic fluid. Retinol in amniotic fluid obtained at 16 to 18 wk from pregnancies that ended in anencephaly or other congenital defects ranged from 2.3 to 18.0 micrograms/dl. The range of amniotic fluid values in abnormal pregnancy precludes using retinol or retinol-binding protein as a marker in prenatal diagnosis of abnormalities.