Recent developments in fetal nucleic acids in maternal plasma: implications to noninvasive prenatal fetal blood group genotyping

The discovery of circulating cell-free fetal DNA in maternal plasma has opened up new possibilities for noninvasive prenatal diagnosis. Fetal DNA in maternal plasma has been used for the noninvasive prenatal determination of the RhD status of fetuses carried by RhD-negative pregnant women. In such analysis, the possible need of an internal control for the presence of detectable amounts of fetal DNA in a particular maternal plasma sample has been actively discussed. Recently, the development of a robust method for discriminating single nucleotide differences in plasma DNA using single allele base extension reaction (SABER) followed by matrix-assisted laser-desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS) has opened up the possibilities of using a panel of single nucleotide polymorphisms as such a positive control. A second approach is the recent successful development of fetal epigenetic markers which can be developed into universal fetal DNA markers. These developments hold promise to allow the eventual widespread utilization of maternal plasma DNA analysis for the noninvasive prenatal diagnosis of blood group mismatches between the mother and fetus.

Non-invasive antenatal RHD typing

The existence of cell free fetal DNA, derived from apoptotic syncytiotrophoblast, in the maternal circulation has opened new possibilities of non-invasive prenatal diagnosis. Although still some technical problems exists, especially the lack of a generic positive control on the presence of fetal DNA and the aspecific amplification of background maternal DNA, non-invasive prenatal RHD typing has been successfully introduced in several laboratories, especially in Europe. The diagnostic accuracy reaches>99%. In the Netherlands PCR guided administration of antenatal anti-D prophylaxis is cost-effective and nearby. In this review the main characteristics and applications of cell free fetal DNA are discussed, with an emphasis on prenatal RHD genotyping.

[Analytical validation in erythrocyte immunohematology]

In a transfusional or foeto-maternal context, hemolysis by incompatibility due to anti-erythrocyte antibodies (regular or irregular) remains the most frequent and most serious immunological risk in the receiver. In order to prevent this risk, a number of actions must be taken, such as the realization of the immunohematologic analyses for which the methodological practices have been legislated because of their serious clinical consequences. Several elements play a role in the reliability of the analyses and their results: the selection of the reagents and their validation in the routine technique used; the validation of reception; the controls involved in secondary preparations (e.g., blood cells reagent); and the daily internal controls. All this requires the choice of adapted controls and the management of possible anomalies.