PRENATAL COUNSELING

False negatives have graver clinical implications. Misidentification of an RhD-positive fetus as RhD-negative could prevent that fetus from receiving appropriate surveillance and intervention. False-negative assessments from ffDNA are probably caused by poor amplification of the test sample.

Safeguards have been used in most protocols, including tracer mouse DNA as an internal control to assure amplification. Simultaneous SRY gene testing assures amplification of male fetal DNA. For females, incorporation in the amplification assessment of highly polymorphic markers different from those of the maternal sample may verify fetal DNA amplification.

What is ahead?

Protocols to refine use of ffDNA for RhD genotyping are likely. Meanwhile, techniques are being modified to assure extraction of sufficient quantities of fetal DNA.

Future research will focus on quantitative changes in ffDNA as a marker for pregnancy complications, and development of noninvasive prenatal assessment of specific genes. Successful development of a noninvasive ffDNA diagnostic test will enhance prenatal evaluations without the risk of pregnancy loss currently associated with amniocentesis and chorionic villus sampling.