delta optical density analysis [Gk, delta, fourth letter of Greek alphabet, optikos, of sight; L, densus, thick; Gk, a loosening] , a technique used to diagnose anemia in a fetus by measuring the proportion of bilirubin decomposition products in the amniotic fluid. The method involves spectrographic examination of a fluid sample. It measures the bilirubin and bilirubin-products concentration according to the wavelengths of light absorbed by the hemolytic products, as the bilirubin products alter the normal color of the amniotic fluid. The data are sometimes expressed in terms of δOD450, the number representing the wavelength in nanometers at which maximum absorption of light by bilirubin occurs. If the delta optical density analysis indicates the fetus is moderately to severely anemic, immediate delivery is usually recommended when the gestational age permits. Otherwise, intrauterine fetal blood transfusions may be recommended.
