Discordance in deoxyribonucleic acid analysis of fetus and trophoblast

Molecular analysis of deoxyribonucleic acid extracted from trophoblast has become an important component of modern prenatal diagnosis. Discrepancies between trophoblast and fetal tissue in both chromosomal and metabolic analysis have been reported. We studied 50 paired fetal and trophoblast deoxyribonucleic acid specimens with a highly polymorphic probe for repetitive "minisatellite" regions of deoxyribonucleic acid that may be areas of high recombination. Four pairs showed persistent variations in bands consistent with differences in fetal and trophoblast deoxyribonucleic acid. Discordance in trophoblast deoxyribonucleic acid as a reflection of fetal genotype may be secondary to mitotic recombination or sister chromatid exchange in the trophoblast, and the possibility of discordance must be considered in interpreting the results of prenatal diagnostic testing on trophoblast specimens.