Can a single measurement of amniotic fluid delta optical density be safely used in the clinical management of Rhesus-alloimmunized pregnancies before 27 weeks' gestation?

BACKGROUND

To assess the efficacy of a single measurement of amniotic fluid optical density deviation at 450 nanometers in predicting fetal anemia in Rhesus-alloimmunization before 27 weeks gestation.

METHODS

In this cross-sectional study, fetal blood and amniotic fluid samples from 43 Rhesus-alloimmunized pregnancies at 18 to 26 weeks gestation were obtained under ultrasound guidance. Amniotic fluid samples were scanned by spectrophotometry for optic density at various wavelengths. Deviation at 450 nanometers was calculated between 550 and 365 nanometers. The fetuses were divided into three groups based on their hematocrit levels and the predictive efficacy of optic density zones for anemia was evaluated.

RESULTS

A high number of false positive and false negative results were observed when the delta-amniotic fluid optical density of fetuses at risk for anemia was plotted to the zones recently proposed to manage Rhesus-alloimmunized pregnancies.

CONCLUSIONS

These data confirm previous results that the diagnosis of fetal anemia in Rhesus-alloimmunized pregnancies before 27 weeks' gestation cannot be accurately made by a single measurement of amniotic fluid optical density at 450 nanometers.