Prenatal diagnosis of the Rhesus D fetal blood type on amniotic fluid in daily practice.

Objective: To retrospectively examine the diagnostic accuracy of prenatal RhD blood type genotyping on amniotic fluid, using a combination of two polymerase chain reaction (PCR) methods in daily practice.
Methods: Amniotic fluid was obtained from women undergoing amniocentesis. Two PCR protocols were carried out in two different laboratories. We obtained the postnatal serological RhD status. In cases with differing prenatal and postnatal test results, we investigated the possible error source by different methods. Sensitivity, specificity and the predictive values were calculated.
Results: Prenatal RhD genotyping was applied in 1,640 cases, of which the postnatal serologic RhD status was obtained in 927. No discordance between both PCR methods occurred. In nine out of 927 cases differing results between PCR and serologic status were encountered. The sensitivity was 99.5%, the specificity 98.6%, and both positive and negative predictive values 99.1%.
Conclusion: Prenatal diagnosis of the fetal RhD blood type with PCR from amniotic fluid is highly accurate in daily practice and associated with a minimal sensitivity of 99.5% and a minimal specificity of 98.6%.