Deviation in amniotic fluid optical density at a wavelength of 450 nm in Rh-immunized pregnancies from 14 to 40 weeks' gestation: a proposal for clinical management.

OBJECTIVES: Our purpose was to study deviations in values of amniotic fluid optical density at 450 nm in Rh-immunized pregnancies in the second and third trimesters and to propose a clinical management plan.

STUDY DESIGN: A total of 789 amniotic fluid single and serial values of deviations in optical density at 450 nm were performed on Rh-immunized pregnancies from 14 to 40 weeks' gestation. The relationship of the deviations in amniotic fluid values of optical density at 450 nm to varying degrees of fetal disease were examined.

RESULTS: In Rh-negative fetuses (unaffected) amniotic fluid values rise until 22 to 26 weeks before decreasing to term. In fetuses at risk of dying in utero, values are higher and trends rise. A clinical management plan was devised on the basis of the amniotic fluid findings of deviations in optical density at 450 nm.

CONCLUSIONS: A clinical management scheme consisting of four zones is outlined. Rh-negative fetuses have minimal invasive procedures. Fetuses at risk of death undergo early cordocentesis for evaluation and therapy. Values that fall in between can be separated into two zones on the basis of the degree of risk.